Prestige Classes and Multiclassing
Incarnum didn't get much love, and meldshapers don't multiclass well.
Still reading? OK, it means you've got a specific goal in mind and want to make it work. Here's a few recommended PrCs and multiclass options for you.
Incandescent Champion: Not very good (pardon) for an Incarnate due to lack of soulmeld progression and mediocre class features. You can't enter it before 12th level anyway.
Incarnum Blade: In the original handbook, I gave a solid review of this class. I stand by that review. It just plain old sucks for a pure meldshaper entry, and the Blademeld Chakra abilities aren't that good.
Ironsoul Forgemaster: Out of all of the PrCs for an Incarnate, this one is great. You lose a level of progression, but the ability to craft magic items is undoubtably the best ability for you. Talk your DM into letting you apply special abilities to your Incarnate Weapon soulmeld instead of making an actual magic weapon, and it is even better! The same effects can be obtained through Legacy Item rules and Kensai levels, but this one actually progresses your meldshaping (and gets you the Heart chakra a level early). Dragonborn Dwarf is the best entry, and it makes a great Tanking PrC due to improved BAB.
Necrocarnate: I deconstructed this PrC in a different thread. Let me find that post. The basic jist is that this PrC is always a level behind in chakra binds, soulmelds, and never gets permanent essentia. That last part is the real kicker. Never mind infinite abuse when you can't even kill something during your first encounter each day. The extra Zombie is nice, but not needed. It's possible to use this and Totemist to get access to every single Chakra Bind and Soulmeld in existence, but thanks to a lack of easy essentia you're going to be spending most of your GP on Wands of Soul Boon and Essentia Helms, along with needing some random mooks to off every now and again. A Thrallherd in the party will help with that last option, as will anyone who wants to abuse Planar Binding+Animate Dead.
Sapphire Hierarch: Optimal entry is Ur-Priest, but that requires alignment house rules (shifting the SH or Ur-Priest to either Evil or Lawful, respectively). Cleric entry works too, but don't focus on the Incarnate side too much (as you won't be able to progress it any further after 10th level, at least not without Epic rules and such). The class features are fairly mediocre, but the spellcasting is all you care about. The Incarnum Domain has Incarnum Apothesis, which can be Persisted for great fun. Meldshaping is a great way to augment your Divine abilities, and a DMM: Persist Cleric with soulmelds is pretty scary. The only complaint is the lack of Chakra Bind progression, but spells again make up for most of that.
Soulcaster: Take it to 7th or 8th level, then PrC out. That's all its really worth to an arcane caster. Gnome is the best race for this PrC, and Incarnate 2/Wizard 5/Soulcaster 8/Shadowcraft Mage 5 is the best build for you (despite the 2 level drop in CL). Kobold Sorcerers can pull some shenanigans (I told you they were better at everything) to get 16th level meldshaping advancement and 9th level spells, pretty much the best deal you can get pre-Epic.
Spinemeld Warrior: I don't recommend Incarnate entry here, unless your DM has a homebrew Dual-Advancement class for Meldshapers.
Totem Rager: Leave it for the Totemist.
Umbral Disciple: It isn't exactly a good Prc for a dedicated meldshaper, but if you dipped into Incarnate and don't have spellcasting or similar abilities, this PrC is rather nice.
Witchborn Binder: Ahh, useless. I love how they make a PrC to combat spellcasters that relies on your meldshaper level, then cuts 4 levels out of your advancement. In effect, this is a massive nerf. Not worth even dipping. The Dispelling Orb is nice, but you can just leave it to the full casters. If it had 8/10th advancement, Chakra Bind progression, and made up for the lost levels with a boost to your Meldshaper level (because the spellcasters can boost CL easier than you can sneeze), it wouldn't be half bad (possibly even worth it). But it sucks.
Legacy Champion: Even if you can't designate a Soulmeld as a Legacy Item, I'm sure you can craft a custom one that will be worth while. The key here is the UMD as a class skill and 8/10s Soulmeld/Chakra Bind progression with Medium BAB. Losing the Soul chakra kinda hurts, but you can make up for it threefold.
Kensai (Complete Warrior): For the melee builds. If you can talk your DM into treating your Incarnate Weapon as your signature weapon (which really makes sense), this is an ideal PrC for a Lawful Neutral Incarnate. You can boost your Concentration checks using the Vitality Belt and Lucky Dice. If this flies with your DM, Chaotic Neutral is also viable because of Legacy items. I don't recommend more than a few levels (and Incarnate can't enter easily). 3 at most, and take the Skillful Enhancement from Complete Arcane. A build I've thought about in the past was Incarnate 16/Cloistered Cleric 1/Kensai 3, which works out nicely and sets you up for Sapphire Heirarch in Epic play.
Apostle of Peace (BoED): This is a somewhat broken, somewhat crap PrC. Its a wannabe Ur-Preist for NG, but the spell list is more limited. Thankfully, it makes up for this with Vow of Poverty and Peace and Nonviolence, and by breaking VoP's restrictions somewhat. The bad news is that you can't hurt people, the good news is that you can be a DMM Healer, Buffer, and Diplomancer at the same time. I myself ban this PrC for various reasons (mostly due to the inter-party strain and the headache concerning the WBL restrictions).
Ur-Priest (CD): Tiefling Incarnate substitution levels get you the required skills and saves, so all you need are the feats. Get the Incarnum Domain through Divine Oracle, devote yourself to an Elder Evil, and ask your DM to reflavor the Sapphire Heirarch to NE instead of LN. Two of these are RAW, one of these is house rules. Regardless, even straight Incarnate 10/Ur-priest 9/Divine Oracle 1 is great.
Home Brew: There may be some PrCs out there that someone else made, or there may be one you or your DM made. If it matches up fairly well to the recommended PrCs listed above, then it may be worth taking. If it matches up to the ones that I told you to avoid, don't bother.
Multiclassing in General: Very little should be used unless you know what to do/avoid doing. Because so little advances your meldshaping abilities, I mostly recommend not multiclassing at all and taking Leadership to make up for it. However, there's times when Multiclassing is the best option. Level dips into Incarnate are very powerful despite what you lose, and Soulcasters/Sapphire Heirarchs are very well-off taking 2 levels in Incarnate (Totemist is fine too, but this handbook is about Incarnates). Factotum 1+Able Learner (Races of Destiny) is an excellent level-dip costing you only your capstones (one is good, the other is ok, both can be saccrificed) at the benefit of making you Skill Monkey GOD. Totemist 2 also makes a good dip, replacing your Soul Chakra with the Totem Chakra (works best with NE and LN Incarnates). Kobold Incarnates may want to go Sorcerer/Soulcaster and grab Greater Rite of Passage and Loredrake to make up for your 4 or 6 Incarnate levels (6th level offers an extra Chakra Bind, and 16th level offers 8 soulmelds, 18 Essentia, and 4 chakra binds as opposed to 12th level's 7, 12, and 3).
Gestalt: I mention this because I use it, and many other people like it. Gestalt is Incarnum's playground, allowing you to either test out Incarnum itself or optimize the unholy hell out of your stats. Really, Incarnate goes good beside mostly every other class, and doesn't ask much in exchange (you just need to put a little into Con). This is a list of potential Gestalt Builds and how they work. All of them assume the other half is pure Incarnate. Seriously, Gestalting Incarnate is a great way to boost your abilities, even if you aren't that good an optimizer.
Wizard: GOD, but with more GOD. Less buffs are required, and your Familiar is now worth keeping no matter what (seriously). This is a potentially broken combo if you know how to play a Wizard, as you can shift between any party role almost spontaneously.
Sorcerer: Kobolds love it, and its almost as good as Wizard. Cha/Con doesn't boost much though, and your saves, HD, and BAB aren't going to be that high. Still, potentially good.
Cleric: An obvious choice due to stats and alignment. DMM is your best friend here, as is Midnight Metamagic. Your HD improves and so does your BAB (unless you use Cloistered Cleric, which is worth considering). Regardless, Divine Power=Win.
Druid: Another obvious choice, but for a different reason: Wild Shape. Your soulmelds still function provided your new form has the required limbs to hold them (as defined by Chapter 7 of Magic of Incarnum), meaning you can assume any Bipedal or Quadrapedal form and keep them active. Elementals and Plants are a bit tricky, but most outsiders and Giants (MoMF and Planar Shepherd) will be OK. Your Animal Companion will also benefit if you play it safe. A small race may be best so you can use your Companion as a mount for the first few levels.
Fighter: Its a tad dull, but your stat pumping abilities on the Incarnate's side mesh well with the Fighter's bonus feat progression. Choose carefully and you will be able to outgun any encounter.
Barbarian: Soulmelds don't require Concentration checks unless you get caught shaping them or need to rebind them you'll be fine. Rage also boosts your stats, but Chaotic Neutral is a bit restrictive and fairly dull. Maybe not worth it, but it depends on what your party needs most.
Monk: One of the many potential fixes is to use Gestalt and add Incarnate to the other side. Not worth taking Monk to 20th (as Dman's handbook has told us), but worth looking into.
Bard: You can become the ultimate party-buffer. Plus, spells are always welcome for an Incarnate. Better BAB, better skill selection, at the cost of a little MAD.
Rogue: And we have a potential winner! 8+Int skills, good Reflex, and a better BAB than the Incarnate. Plus it works with every alignment in some way. Can't go wrong, ever.
Ranger: Somewhat a mix between Rogue and Fighter. At least the Animal Companion won't suck like it usually does. TWFing or Ranged, your choice. May want Swift Hunter though, and the Wild Shape variant in the SRD is absurdly good for this combo.
Paladin: No.
Soulknife: ...Seriously? Use PsiWar instead. Exception: Soulbow.
Psychic Warrior: Fighter+Psion/2=Awesome. Between your bonus feats, powers, BAB, and Soulmelds, you will be a house of pain. Any alignment works, and there's even Ability Synergy.
Psion: Like Wizard, but Psionic. Nothing else to say here.
Wilder: Meh, a step down from Psion or PsiWar IMO, but it could work. The problem is you can't spare feats for your Incarnate side.
Ardent: A smaller step down from PsiWar than Wilder, but better than the Wilder IMO. The biggest boon is that your manifester level determines how you learn powers, so it works nicely. There's no limit to the number of ways to play this combo, so feel free to mess around. Always take EK: PsiReform though. Also, Customize your Mantles using Mind's Eye
Divine Mind: Eww, no.
Lurk: Many people recommend the Psionic Rogue over this, and I frankly agree. The Psi Rogue is online for free, and is an excellent class (it should be equal to the Rogue, IIRC).
Erudite: Wizard+. Its broken as written both ways, so do you and your DM a favor and don't use it.
Crusader: Flavorful, powerful, and nearly unkillable if built right. A great choice for melee, and Stone Power+Cobalt Power is kinda mean. Incarnate is a natural choice for this. MAD may show up if you focus on Cha-based abilities like Smite, but you can make up for that.
Swordsage: Almost as natural as Druid, and an improvement to everything. Between a massive number of maneuvers known, the best meldshaping abilities in the book, and the freedom to choose whatever feats you want, this is an amazing choice. Totemists like it too.
Warblade: Equal in almost all respects to the Crusader, and the Int focus is more useful than the Cha focus. A bonus to everything that rivals the Swordsage too. Your class features stack with your meldshaping abilities, and you are very versatile. The only problem is the recovery mechanic uses a Swift action, meaning your Incarnate side can't switch essentia around when using it.
Dragonfire Adept: 1) UMD as a class skill. 2) Con-focused. 3) Everything BURNS! Its kinda hard to mess this combo up.
Warlock: Flavorful too, and equal to the DFA if built right. The problem is a questionable ruling on the Strongheart Vest+Hellfire Warlock, but even if it gets denied you still have the best UMD check in the game. And the Sighting Gloves arguably apply to EB due to it being a Ray.
Warmage: One soulmeld boosts your damage, but this is more limited than a Sorcerer. If you think about using this, consider just playing a Sorcerer or Wizard with Focused Specialist instead so you don't get screwed with your spells.
Wu-Jen: Never been partial to them.
Favored Soul: A step down from Cleric, but still very potent.
Spirit Shaman: A step down from Druid, but notable in that it keeps the spell list. If your DM is afraid of your optimization skills, this may be the safer choice. Some feel this is still Tier 1 material.
Shugenja: Its Tier 2, but barely. It got no love, unlike the Wu-Jen. Spirit Shaman is the better choice here.
Totemist: This is a difficult combo to make work due to Soulmeld restrictions, but if you shape them carefully you may be able to pull it off. Ask around CO for help with this, and note that you will be taking Double Chakra a LOT.
Soulborn: Possibly fortunatly, this can't be done as per RAW. The class is kinda weak anyway; you'd end up being better off with Ranger in the long run.
Incarnate: If only...
Binder: More flavor love, and a class that neatly compliments your versatility. Look into this combo.
Shadowcaster: Kinda good, kinda weak. A step down from Sorcerer in my experience.
Truenamer: Its possible to fix the class using Incarnum, provided you home brew a soulmeld or take the Item Familiar feat and run with it. Not a good combo if you can't.
Hexblade: Use one of the various fixes please. Still, even without them you've got access to Polymorph.
Swashbuckler: Made possible thanks to Daring Outlaw in CS, this is an alternative to Fighter, Ranger, or Warblade.
CW Samurai: Lawful syngery, but sucks. You'd be more focused on Incarnate than this, but could pull it off.
Factotum: A personal favorite class, this is better than the Rogue thanks to its skill selection and class features. You can't possibly suck with this combo unless you tried.
Scout: It honestly works better with Totemist.
Spellthief: A weak class, but if you're in a high-magic campaign and face spellcasters regularly, this+Incarnate=Powerful. Its a step down from Rogue in some ways, but it makes up for it if you are careful.
Ninja: There's a little synergy between the two. Notably, you can make up for this class' inherently weaker Sneak Attack with Incarnum abilities.
Artificer: Hello broken! My name is your best friend. These two classes were practically made for each other. UMD boosters, skill boosters, magic items galore, and abilities abilities abilities. The only problem? Complicated six ways to Sunday. Be prepared to give your DM a headache unless he's intimately familiar with both classes.
Archivist: Its like a Wizard fucked a Cleric and stole the child. Seriously, this class is for you.
Dread Necromancer: Necrocarnum fun, but you don't have to be Evil for this class. Never take it to 20th though, as Lichdom itself screws your Incarnate half.
Beguiler: A mix between Wizard and Rogue. Not the best of both worlds, but good enough to make up for it.
Dragon Shaman: I recommend DFA over this class, but there's nothing stopping you. It can play like a gimped DFA/Tank.
Duskblade: Duskblade is a fusion of the Fighter and Wizard, and Incarnate makes this class really powerful. Consider it strongly. NE+Full BAB=Death.
Knight: Lawful Neutral is manditory, but the class features make up for this. Its a step down from Crusader, but it has abilities unique to it to make up for that. Grab Wild Cohort and you can be the ultimate Paladin.
Other: DMs are strange. They allow the weirdest things from home brew. Look at your options and the list above, and consider where the class he provided you falls. If it stands at least a step down from the class you compare it to, consider trying it out over that class (unless I said no to the class you compared it to or if Alignment is a problem). If its lower than that, don't bother.