I'll just copy and paste a reply I made when someone asked me a similar question:

I'm a firm believer in getting the defenses before getting the nifty stuff.  When I AAed my Enchanter (who, for the most part, has everything he needs), defenses came first.  You can't help anyone with anything if your toon is dead. So things like Combat Agility, Combat Stability, Run 5, Eldritch Rune (at least till level 8 so you can get...) Veil of Mindshadow (80% mitigation to 3000 HP + 500/rank), Hastened Veil of Mindshadow will reduce the reuse time of Veil of Mindshadow by 30 seconds per rank.  VoM's normal reuse is 10 minutes. Shield Block (obviously, you need a shield, and this AA will block ~5% of incoming hits).  While I consider these your defensive priorities, no list of defenses would be complete without Spell Casting Subtlety.  Your tanks will thank you.  I hesitate to recommend Mind Over Matter, because I hate the thought of splitting incoming damage between my health and my mana, but I can't deny that it's saved me more times than I care to count.  But BLEAH!  Leave my mana alone!  Color Shock is an activated AA that has a chance to stun any mob that hits you.  Since the introduction of the Ward line, I wouldn't consider that important, but it can be useful, due to the crappy duration of the Ward, you might need it once in a while, or if you're planning on stopping a train. Doppelganger shadowsteps you, leaving a simulacrum of you in your place (4th rank will conjure a second one).  These clones are not terribly resilient and get struck down rather quickly.  They will buy you enough time for one uninterrupted cast.  Beyond that, all bets are off.

After defenses comes mana.  Granted, most styles of play are not mana intensive for an Enchanter, but some are, including mine.  Spell Casting Mastery, when maxed, will reduce the mana cost of spells by 10%.  Mental Clarity will increase your mana regeration by 1 point/rank.  Expansive Mind raises the cap of mana regeneration allowed by gear.  Gather mana, to recover 10K mana; Hastened Gather Mana, to shorten the reuse time; and the vastly more powerful Mana Draw, which will recover 20K mana (when maxed), plus give you enhanced mana regen for a full minute after use.  Azure Mind Crystal to store a small bit of mana for use during crunch time.  Gift of Mana line allows you a chance to cast your next damage spell for only one point for a limited time.  Huge mana sink, however.  You'll have to buy ranks that you've already outgrown just for current ranks.  Wouldn't call that last one too big a priority.

Now that you've made sure that you will never die and always have mana, the functional AAs.  Beguiler's Directed Banishment, by consensus, seems to be the most powerful AA in our arsenal.  Knocks back mobs for 14 units, roots them for three ticks, then blurs them with 100% reliability.  In other words, it knocks a mob out of aggro range and makes them forget all about you.  Beguiler's Banishment is an AoE cone of the same AA that will strike up to three opponents in front of you.  Self-Stasis will mezz you for about 6 ticks and clear all aggro.  Phantasmal Opponent will create a clone of the mob you're fighting.  The P.O. has a trivial amount of DPS, but 100K HP. Deep Sleep is a potent debuff that will reduce a mob's attack rating by 3%/rank and has a 3% chance/rank of proccing when you cast a mezz.  By using this AA with Stasis (another AA you should get, which is a 3 minute mezz with a 1K resist mod that caps at 73), you can get Deep Sleep to land by repeatedly casting Stasis (since it caps at level 73,  it will not mezz most the mobs you encounter at your level) till it procs.  Nightmare Stasis is a three-minute, 1.5-second cast mezz with a 1K resist modifier.  Mobs awoken from this mezz will be slowed and snared (Waking Nightmare is the name of the recourse) for one minute.

There's also a number of AAs that are useful because they replace spells.  Perfected Invisibility is a fast-cast (not instant) version of improved invisibility, comes in a group version, too.  Perfected Levitation (will have a group version next expansion), .1 second cast self-only levitate.  Can be cast while running.  Gate is a 2.5 second cast version of the same spell.  Fog of memories is an AA blur.  (You'll need Enhanced Forgetfulness, which will improve the chances of blurs landing successfully by 5%/rank. With this  AA,  FoM has a 95% chance of success.)  Summon Companion will bring your pet (including a charmed mob) to your side and is instant cast.  There is also Focus of Arcanum.  Strictly speaking, Focus of Arcanum is not a spell, but it is a clicky that has been featured in Enchanter lore, such as our Anguish Robe and TSS clicky robe, it increases the chances of your spells landing.  Bite of Tashani is a useful AoE Tash that is a nice complement to your AoE mezz.  Edict of Command is okay.  It's a six minute timed charm that will charm up to 85 (the only charm in game that will do so),  but it's got a monster reuse time of 72 minutes,  reduced to  63 with AAs, and a long cast time.  Plus you need that "Ode To Suck" AA, Dire Charm, to get it.  If only we could have our cake and Edict, too.

But these are all activated abilities.  There's passive AAs that are also useful.  Total Domination will reduce the numberr of charm breaks.  At maxed level, it has a 50% chance of preventing a charm break that would have otherwise occured.  I'm guessing the base chance is 25%, with 5% per additional rank.  Mesmerization Mastery will improve the duration of all mezzes by one tick/rank.  Very useful with your PB AoE mezz, as this normally last one tick.  But with maxed MM, you will recover the mezz before  it wears off, in theory allowing you to keep an infinite number of mobs mezzed indefinitely, as long as they're surrounding you. Mnemonic Retention, to give you extra spell gems. Auroria Mastery will be appreciated by your groups, as we're the only class who gets this ability to maintain two auras at once.  Already mentioned Enhanced Forgetfulness.  Spell Casting Reinforcement and Spell Casting Reinforcement Mastery to extend the duration of your buffs.    MGB and Hastened MGB.  I'll let you decide how important that is to you.  How much raiding do you do? Finally, I don't care how much anyone on this board screams and cries every time I mention this AA, Planar Power will raise the stat caps of all statistics.  While most stat increases do virtually nothing for you after around 250, Charisma is apparently the one exception.  An estimate done over at therunes.net suggests that for every ten points of Charisma, the mob has a -1 on its resists to your charm, mezz and also you're less likely to get resists or trains on your pacification line of spells.  So, while Planar Power sucks, it sucks