Dread Necromancers have a few chances to add any Cleric or Wizard/Sorcerer Necromancy spell to their spell list via Advanced Learning. At each opportunity, they get one spell of their choice, but the spell level they can cast or lower. The following is a list of solid Dread Necromancer Advanced Learning spells to grab. As for the rest of how to play a Dread Necromancer, you'll have to look elsewhere.
#1 (level 2-):
Ghoul Glyph. A handy spell out of Spell Compendium that does something none of your other spells do. This one leaves a permanent glyph that, if anyone but you gets to close to it, paralyzes a victem for a few rounds. The glyph can't move though. Combined with water filled pit traps you've got yourself a very lethal trap. Also, nothing stops you from placing multiples of these on such traps... enemies might make one save, but they won't make 5. This is also a great way to burn unused spellslots at the end of the day, creating rings around you for safety. It's obviously handy in ambushes, and it's especially useful if you want to start casting Planar Binding (remember, you don't have Magic Circle spells, so anything you Bind must be killed and reanimated to be useful. This is much easier if they get instantly paralyzed on the way in).
Kelgor's Grave Mist. Players Handbook 2 has this gem, which is a long range AoE that fatigues enemies and deals 1d6 cold damage per turn. Remember that skeletons are immune to both fatigue and cold damage, making this a great one to throw into a fight. No save, too. Just create an area of the battlefield that keeps enemies from charging. It's a wonderful way to slow down an enemy Frenzied Berserker.
#2 (level 4-):
Black Sand. This spell out of Sandstorm is absolutely incredible. It's an AoE effect that deals 1d6 points of negative energy damage to everyone in the area per round for caster level rounds. Also, it creates a darkness effect. Thus, it heals your minions and hurts enemies. More importantly, however, anyone killed by it permanently turns into Black Sand. As such, you can now put this generated sand in the boots/body of any of your minions (and maybe in your boots if you have Tomb Tainted Soul) to gain fast healing 1d6, permanently. Awesome. Also, the spell itself can be made permanent if you lack bodies to turn into the stuff, and this is great for making fortifications.
Consumptive Field: Get a huge caster level the fun way. Combine this with Kelgor's Grave Mist or Black Sand to kill off a bag's worth of rats and go to town. Libris Mortis and Spell Compendium have this one.
Delay Death: A buff that lets an ally simply not die. Very useful in general. The duration isn't very long, though.
Shivering Touch: An old favorite from Frostburn, this lovely spell deals 3d6 dex damage on a touch attack with no save. Brilliant! Teach those dragons a lesson. Combine it with Black Sand (above) to take out the now helpless enemy and congratulations, you have permanent black sand.
Skull Watch: Tired of DMs sending enemies to jump you when you're trying to covert your party into Necropolitans or researching new monstrosities to create? Then this spell is for you. It's permanent, and it'll warn you when enemies show up. Just make a bunch of these and set them out when you need to establish a safe perimeter. It's found in the Spell Compendium.
Undead Torch: Originally from Ghostwalk, this spell is a one round per level buff of an undead critter that causes the critter to deal an extra 2d4 damage to with all melee attacks, and if the critter dies, people passing through the space take damage. Generally, this is unimpressive, but on a hydra the extra 5 damage per hit adds up fast. I'd have a tough time taking this over Black Sand for the purposes of buffing undead, though.
#3 (level 6-)
Animate Dread Warrior: Endless source of intelligent undead that still have their abilities from life? Yes please! The Exp cost stinks though, so this is a good choice for Spell Stitching if you have that option. Unapproachable East has this spell.
Door of Decay: From Complete Champion, this spell lets you teleport from one of your undead to another. It's great if you have a home base... just leave one skeleton back home to use as a gateway. It definitely adds something new to the list.
Haunt Shift: This gem from Libris Mortis is wonderful for anyone with a good imagination. Getting tired of enemies using Turn Undead? Create a statue of a skeletal warrior out of adamantine, then use Haunt Shift to animate the thing and send it into battle. It's a construct now with a Hardness of 20. No one ever expects that. Great for making ultra tough tanks... or traveling around in a haunted carriage for pure style points (note: a Porpoise skeleton has very few HD and a movement speed of 80, making it perfect for haunting your carriage). Note, if you're creating battle minions with this spell through the use of statues, take note of the spells Shrink Item (Permanent!), Invisibility (which can be made Permanent on objects), Augment Object, and Hardness, as well as the psionic power Matter Manipulation. You can't have these spells, but a friendly Wizard, Archivist or Psion might, and this can create all sorts of fun involving invisible size changing minions with a hardess in the hundreds.
Touch of Vecna: This one from Complete Mage is certainly fun. A touch attack deals 1d8+10 damage and makes the target shaken for one round, and then if they fail a fort save they're paralyzed permenantly. Okay, seriously? Shaken with no save is awesome, and now if your fear aura hits them (at -2 saves) they're frightened for a good long time, so even passing their save on this spell leaves them pretty screwed. Also, you did take Sickening Grasp as a feat, right? So they're at -4 saves after this? Yeah, good times. Plus now your familiar can paralyze them if you have a Ghostly Visage. This spell combined with your other Dread Necromancer abilities is just incredible as a nearly gaurenteed killer. Throw in some armour with the Fearsome enchantment so you can intimidate as a move action and you can now get them even more afraid when you cast this. Very fun. Of course, if they do fail the fort save then yay, your castle has a brand new statue. Or you can kill them with Black Sand to get more of the stuff. Or sacrifice their soul for crafting exp, and then raise their body in service to your evil whims. Or construct a catapult and chuck them back at their friends with an Explosive Runes parchment shoved in their mouth. Whatever. Point being, they're your toy and you're a necromancer. Whee! Note: this sort of behavior is not appreciated by the party Paladin. You may have to use this spell on him next.
#4 (Level 8-)
Arrow of Bone: This one from Spell Compendium is handy if you're in a party with an archer or assassin. Just enchant a few arrows with this spell ahead of time (heck, do it the day before, by the time you have this spell it lasts a minimum of 16 hours!). Now you can shoot down any one enemy from long range, and they're GOING to fail one fort save if you make them take four or five. But really, this is a bit situational, so it's only appropriate if you need to drop BBEGs or otherwise assassinate targets.
Avascular Mass: Another Spell Compendium bit of fun. A ranged touch attack which, with no save, halves enemy hitpoints and leaves the target entangled. Also, the target must fort save or be stunned for one round, and people nearby must reflex save or be entangled, plus even if you pass the save you have to make strength or escape artists checks to move. REALLY nasty and a great way to take a lot of enemies out of the fight for a while... just blast the BBEG and he's screwed even if he makes his save, and you'll handle his melee mooks in the same shot. And you just ripped the blood vessels out of the enemy and tangled up their mooks in the ripped out body bits. Style, baby. Oh, and don't forget to cast Cloudkill on the now entangled target. One warning though: you can't see through the mass well, so the target will have total cover. Then again, so will you... to the target. That could help or hurt.
Avasculate: A weaker version of Avascular Mass, this spell doesn't entangle or have AoE effects, but it's one level lower. Personally, I prefer the mass version since the added debuff and AoE is awfully nice, but this way the total cover issue goes away.
Awaken Undead: Spell Compendium brings us this lovely little thing. Remember, the undead are still under your control, so this is a great way to have hordes of intelligent minions. Very nice!
Blackfire: Out of Spell Compendium, this spell is a medium range ray that deals con damage. Not bad, and the damage can be quite high, up to 1d4 per caster level (though enemies will make some of the saves). Note that the duration of the spell is limited by caster level only, so the damage is actually uncapped, making this a hilarious one to combine with Consumptive Field, making it a great potencial necromancer assassin tool. Just pump your caster level with a CF loop to insane levels (50, let's say?), then snipe the target with Blackfire (at that caster level, your range is 600 feet). The target now takes 1d4 con damage per round (fort save each round, on success they're sickened that round instead of taking damage), and it won't stop until they die or dispel, the latter of which just won't happen (though three saves in a row will put it out... but those are fort saves and you're doing con damage!). Plus, when dead they need a True Resurrection or Wish to come back, with a high caster level check. Yehaw. Also, anyone adjacent has the Blackfire spread to them, which is nifty... you can take out large packs this way. Very stylish.
Consumptive Field, Greater: Everything I said about the earlier version applies here, but this one lets you kill swarms of rats for massive power very quickly. If you've got a way to persist this, you become a god, basically.
Evil Glare: Another Spell Compendium spell, this one gives you a standard action gaze attack for one round per level, will save or be paralyzed for 1d8 rounds (can't hit the same target twice). This means for just one spell slot you can take out tons of enemies... and it works great with a Ghostly Visage and some undead that hits hard. You both stare at the target, and it must make two will saves... if either is failed, it's Coup de Gras time, just order the minion to coup de gras any paralyzed target. Also, with Fearsome armour you can intimidate as a move action if you like, so you can defeat your enemies by being REALLY creepy and staring at them and then if they get close you can leave them cowering (you DO have Imperious Command by now, right?). The range is a bit poor though.
Horrid Wilting: Out of the PHB, this spell offers something few Dread Necromancer spells have: very long range. Plus, it hits a lot of targets (everyone within a 60ft area) without hitting friendly types. So, if you wanted to be a blaster, this would be the spell for you. That said, 75 damage (on average) rarely is worth while at this level, but it's great for clearing out low level enemies or enemies already weakened by other effects, and a Greater Wand of Maximize would get this thing up to 120 damage per target, which isn't too shabby. A second blast would finish off the lot of them.
Kiss of the Vampyre: Another Spell Compendium find, this guy has a lot of potencial for Dread Necromancers. You're already nasty as all heck up close with your Fear Aura, Charnel Touch, and various other touch effects. This one gives you Enervate on all your touch attacks... nifty when combined with your level draining touch attacks that you get anyway as a DN. Also, Gaseous Form is nice for utility, and DR 10/Magic is cute (though pretty worthless at the level you get this). Sadly, the duration is too short for the charm to be of much use.
Necrotic Curse: This Complete Mage spell is hilarious. For 1 hour/level, all positive energy spells within range of you instead deal damage equal to the caster level of the caster. You'll need a high caster level for this to work (hi there, Consumptive Field!) but the results can be hilarious. Cast this spell at the beginning of the day (after the CF power up, of course) so enemies don't see you casting it and don't know it's there. When a big fight starts, launch a Maximized Horrid Wilting (see above). What comes next? The enemy healer fires off a Mass Heal. Heh heh heh. A second Maximized Horrid Wilting should end the encounter. This is also nice in long drawn out fights when your forces are being regenerated by Necrosis Carnexes and Black Sand, while theirs slowly melt away without any ability to heal... but then again, how often does that happen? Still, this spell may be worth it just for the confusion it causes.
JaronK