Getting a mountThis list is by no means exhaustive; let me know if you've found a good source.
PermanentThe best way to get a mount is to have one by virtue of a class feature or feat.
- Animal Companion (Druid): One of the most powerful options. Everything about the druid class is hax, were you expecting any less here? The downside is that you'll need to worry about Handle Animal to control it, unless you combine it with a familiar or special mount (which gives it an Int above 2).
- Animal Companion (Ranger): Not as good, but still respectable. You get an animal companion at 4th level, and use only half your ranger level to calculate its abilities.
- Animal Companion (Prestige Ranger): That's better. This PrC gives you a druid-strength animal companion from lv1. Plus it counts as ranger for most purposes.
- Animal Companion (Urban druidDrComp): Has an alternate list of animal companions, including such things as warhorses, monstrous vermin (though they become Int 1 animals), animated objects and carrion crawlers(!)
- Animal Companion (BeastmasterCAdv PrC): As druid, but add 3 to your class level for determining abilities. Stacks with Druid levels for a very powerful companion.
- Animal Companion (ShamanDr353 cleric ACF): As ranger, but available from lv1; you give up Turn Undead + literacy.
- Buy (gp): You can simply buy a mount with gold - the prices are listed in the PHB. The warbeast template lets buy any creature to serve as a mount but they're ridiculously underpriced, so make sure your DM knows what you're doing.
- Celestial Companion (Holy LiberatorCD PrC): Basically the blackguard's fiendish servant, but celestial instead of fiendish, and its progression also includes +20ft speed.
- Cohort (Leadership feat): The Leadership feat gives you a second character 2 levels lower than yourself. Yes please.
- Cohort (Dragon Cohort feat): Who doesn't love dragons? And in particular, who doesn't love a 3-point reduction in LA for their scaly friend? If your mount is a dragon there's no reason not to pick this feat over Leadership, unless you want an army of followers.
- Dragon (Dragon Steed feat):
- Familiar (Wizard/sorcerer): Familiars usually aren't powerful (or large!) enough to make reliable mounts. They don't get many feats, and their hp is half of the caster's d4 - that's just pitiful. Their ability to share their master's buffs, however, means that they can take advantage of most of the ways the caster has around his own fragility problems - they can do pretty well if polymorphed into something, blurred, etc.
- Familiar (Attain Familiar feat): A duskblade has d10 Hit Dice, so his familiar can actually have decent hit points. Most non-Core arcane casters don't have the same number of buffs though. Note that the familiar from this feat derives its abilities from your caster level rather than your class level - normal familiars aren't advanced by levels in PrCs.
- Familiar (Huge master): From page 203 of the DMG, a Huge or larger character may select proportionately larger familiars - a dire rat, leopard, monitor lizard, Medium owl, Small raven, Medium viper, or wolverine. This isn't for you - it's for a teammate who's small enough to ride them.
- Familiar (Improved/Dragon/Darkness Familiar feats): While these feats can make your familiar large enough to serve as a mount on its own (most of your Improved Familiar options are in Complete Warrior, but imps and quasits have access to Medium alternate forms), it can also be used to open up new types for alter self and similar spells. Familiars with an ECL could potentially be combined with cohorts like paladin mounts can, but it's a grey area so ask your DM.
- Fiendish Animal Companion (Thrall of BaphometDr341 PrC): Like the druid's animal companion, but it gains the fiendish template and your effective druid level is twice your class level (it's a 10-level class). Doesn't stack with druid levels, but PrCs that advance animal companions should still be able to advance it.
- Fiendish Servant (Blackguard PrC): The blackguard's slightly-weaker equivalent to the paladin's special mount doesn't have much support, but it's based on character level rather than class level. Sadly it takes 5 levels and some unusual prereqs to get there, so this doesn't count for as much as it could. You may be able to convince your DM to let you count it as a special mount for combinatory abilities, in which case it gets much better. Going paladin is still easier in most cases though. In addition to the options in Core, you can select a lesser nightmarePlH if you reduce the bonus HD by 2 and your effective character level for determining its abilities by 2. Also take special note of the Improved Fiendish ServantCoR and Nightmare SteedDn100 feats below.
- Flying Mount (SkylordBoED PrC): A celestial giant eagle, celestial giant owl, or celestial pegasus. Progression is similar to a double-speed special mount, but instead of Improved Evasion + sharing your saving throws they gain extra abilities - Improved Natural Attack, Deadly Charge, a flight-based bonus feat, and immunities to paralysis/sleep/charm/compulsion effects.
- Gondsman (TechsmithF&P PrC): It's unclear whether or not Gondsmen have to be humanoid (the fluff makes them sound like an earlier, Forgotten Realms take on warforged), so check with your DM before trying this. There's better options out there unless you're really fond of the "priest of technology" theme.
- Griffin companion (Aglarondian GriffonriderUE PrC): As meaty as a special mount, with double-speed progression but fewer special abilities. Also it's ginormous.
- MagebredECS warhorse (Order of Rekkenmark5N affiliation): Good at low levels, since you get it essentially for free if you write the order into your backstory. The free 4th-level bodyguard at lv1 is kind of cheesy though. Unlikely to get by many DMs.
- Mephit Underlings (Elemental ArchonF&P PrC): A mephit is a pretty awful mount, and its stats don't improve by much, but you get three of them. I guess you could have them pull a sleigh, take the Chariot CombatS&F feat instead of Mounted Combat, and be Fire Santa. Which would be weird and dumb, but still. Three!
- Monstrous Companion (Beast Heart AdeptDung PrC): Pick a Magical Beast from a short list, and it gains 12 levels worth of animal companion advancement in 10 levels. It's not an actual animal companion, so there's no way to advance it further, but the base creatures are stronger than the standard options. You gain two other companions as you gain levels, but at a penalty, so they're useful mainly for utility rather than combat. Your enemies provoke an AoO from you the first time they're struck by one of your companions per round, which is pretty good for a mobile type who won't be in a position to make normal AoOs often. Consider Martial Stance (island of blades) or some other "flexible flanking" ability so you can use Monstrous Flank more easily.
- Party Member (Friendship): If another PC is a horse, then good for you. After all, real men ride each other. Can be very powerful if you get the means to share buffs somehow.
- Psicrystal (Psicrystal Affinity feat): Usually preferable to a familiar. Psions and psychic warriors may not be as powerful as wizards, but the psicrystal's feats, average BAB and hardness give it a big advantage over the familiar, and share pain is a nice buff. The disadvantage is that there are no larger psicrystal variants, so unless your character is very small you will need the metamorphosis power to convert it into a ridable form.
- Spider Servant (Drow JudicatorUnd PrC): Drow only. Grants a myrlocharMoF, a phase spider, a fiendish sword spiderMoF, or a fiendish Large monstrous spider advanced to 8 HD. Includes a progression similar to blackguard, but based on class level rather than character level, and with slightly higher bonuses but no empathic link. Note that both drow and myrlochars are Medium, making them difficult to use as mounts.
- Telthor Companion (DurthanUE PrC): Get any animal with HD up to your class level (including advanced animals) and add the telthor template from the same book (basically it becomes an Int 3 incorporeal fey with telepathy; incorporeality means it needs the Ghostly GraspLM feat or a ghost touch saddle if you're not incorporeal yourself). Fey HD are pretty bad, but the touch attacks compensate for the poor BAB and you could take OtherworldlyPGtF to upgrade to Outsider. Be sure to make use of bloodlines, Legacy ChampionWoL etc. so that you can keep advancing it past lv10, because there's no way to combine it with anything else. Oh, and you get a second companion at higher levels.
- Thrall (Thrallherd PrC): Thralls are like cohorts, but always loyal. A thrall is also one level lower than you rather than two. And if you reach lv10 in the PrC you get another one! The only downside is that you can't combine thrallherd with Leadership. This may not apply to substitutes like Dragon Cohort, but your DM is likely to breathe fire on you if you try it. If you have a psionic build, try to fit a level of thrallherd in instead of Leadership.
- Undead Companion (Death MasterDrComp): A few of the options here can serve as mounts - the wolf skeleton, chimera skeleton (lv -6) and wyvern zombie (lv -6). The extra HD and Str/Dex bonuses follow a similar formula to paladin special mounts, but the special abilities are different. Due to its source, there aren't many ways to advance this companion through other classes, but all the usual tricks for boosting an undead creature apply (the CorpsecrafterLM feat, raising it in a desecrated area, etc.). In any case, you'll likely be remaining a single-class character.
- Unicorn (Beloved of ValarianBoED PrC): The earliest you can get this is ECL 8, and it doesn't have any advancement, so it's more of a utility mount than a combat one. However, at 6th level of the PrC (ECL 13) it receives a massive upgrade, becoming a celestial charger - an 8HD celestial unicorn with 7 levels of cleric.
- Wild Cohort (Wild Cohort feat): Functions more or less identically to a druid animal companion but with no Link, Share Spells or free Multiattack, while its HD, natural armor bonus and tricks known are 1 lower. Grants access to the Silverwood Arcanist PrC for spellcasters.
SummonedIf you're looking at using a summoned creature for a mount, duration is important. If you're using your mount for travel rather than just for combat then a duration of 1 round/level isn't that useful unless you can summon some kind of robot horse with rockets for legs. Bear in mind that you will have to spend actions to get on the mount. And watch out for
dispel magic.
Class features- Celestial Minion (SentinelDr310): This NG variant paladin gets to use any Medium or smaller celestial animal as their special mount, but the duration is halved. This opens up some extremely powerful options (fleshraker anyone?), but isn't compatible with cohort mounts. Plus it's no use as a mount unless you're Small or smaller. Ask your DM if you can combine it with prestige paladin.
- Elemental Minion (IncarnateDr310): The True Neutral paladin (not to be confused with the incarnum class of the same name) gets a Medium elemental as the base creature for their special mount, with the same halved duration as Celestial Minion. Less abusable than the Sentinel ability, but much of the same advice applies.
- Special mount (Paladin): It's a summon, but it lasts 2 hours per paladin level and can be used 1/day, meaning that you can basically keep it up all the time. Of note, according to the DMG you can designate a cohort as your special mount for +2LA - the rules are unclear on whether this creature must be summoned or sticks around.
- Special mount (Prestige paladin): Requires two levels rather than five, one of which advances a divine spellcasting class. You have to wait a few levels to get in - as compensation, your mount's abilities are calculated as if your class level were three higher.
- Special mount (Ranger knightDR317): You know how prestige paladins count as three levels higher? These guys count as five levels higher. Plus since it's built for ranger entry, you have easy access to Devoted Tracker (though it doesn't advance your animal companion in any way). Oh, and the default mount for Small characters isn't a pony; it's a wolf. That's style points right there.
Spells- Astral construct (Shaper 1):
- Call nightmareBoVD (Demonologist 4, Sor/Wiz 5): An evil spell that summons a nightmare for 1 week in exchange for a soul.
- Ethereal mountSpC (Bard 4, Sor/Wiz 4): Like phantom steed but summons multiple mounts. While on the Ethereal Plane they count as CL20 for determining their speed.
- Gate (Clr 9, Sor/Wiz 9): High-level, cheesy, short duration and requires concentration. Pass.
- Hound of DoomCW (Hexblade 3): Summons a dire wolf with BAB and hit points equal to your own, and a deflection bonus to AC equal to your Charisma modifier. Commanded like a fully-trained animal, but counts as a magical beast for spell effects (meaning less potential for buffing). Lasts 1 minute/level, and you can only have one in existence at a time. Oddly enough, it's a shadow illusion but can't be disbelieved.
- Mount (Siyal druid 1, Sor/Wiz 1): Summons a light horse or pony. You can use this from lv1, and it lasts 2 hours/level. Eventually you can summon enough of these for your entire party and keep them up continuously. You can't summon warhorses with this spell, so this is mainly for travel.
- Phantom stagCD (Druid 5): Basically a phantom steed that can also fight, and can cast etherealness at high levels.
- Phantom steed (Siyal druid 3, Sor/Wiz 3): Lasts half as long as mount, but the "horse" it creates is super-fast, can go just about anywhere, and looks cool as hell. It doesn't attack, but it doesn't panic in combat either. Plus "animals shun it and refuse to attack it", which might extend to its rider as well. Gets better with the Knight Phantom PrC (Five Nations) which boosts the CL and gives you extra castings per day. It normally takes 10 minutes to cast, but Knight Phantoms can cut this down to a standard action.
- Planar ally (Clr 4/6/8): Your ally can remain for a number of days, though you need to pay gp and xp.
- Planar binding (Sor/Wiz 4/6/8): Like planar ally, but cheaper and a little more dangerous.
- Summon monster
- Summon nature's ally
Vestiges- Andras: 1/day, for 1 hour/EBL, you can summon a heavy warhorse that comes with a saddle and heavy lance. Of note, this vestige's abilities also include some martial weapon proficiencies and a +8 bonus on Ride checks. It's a 4th-level vestige, meaning you need to be at least a 5th-level binder to get it (or a 7th-level binder if you didn't take the Improved Binding feat); if all you want is the mount then there are better options.
Crafted- Brass SteedHoB: A specialized golem with a market price of 19,000gp. Not the fastest mount around, but its stats are otherwise pretty good, and it gets Run as a bonus feat. Has a listed HD advancement, but the cost of adding extra HD isn't given.
- Clockwork Steed/PonyMM4: A cheap construct mount (2,150gp to purchase, 1,150gp to craft) that takes no actions except when being directed by a rider. Basically it's a horse-shaped motorbike. Comes with a bunch of upgrade options ranging in price from 100~500gp, but unfortunately there's no way to upgrade its HD.
TransformedIf you don't have a creature you can ride, turn something else into one. Many transformative spells have restrictions based on creature type, so that should be the most important thing to bear in mind when choosing a base creature. Many of the same caveats apply here as with summoned creatures - the difference is that if the polymorph runs out you'll still have an ally of some kind.
Some candidates (such as a druid cohort) are capable of transforming themselves, while others require you to cast spells on them. The Share Spells ability makes this significantly easier.
I am the mount!If you're getting a cohort/thrall/etc. it's definitely worth considering making
him the rider and yourself the mount. Alternatively, if your minion ends up significantly more powerful than you (as with the Ubermount and Big Guy Is With Me builds), it might be more enjoyable to play the minion as the main character and the "master" as a tag-along.
On a related note, certain races like centaur count as being mounted at all times due to their anatomy.