I won't be mentioning all of the various profession-only enchants, but rest assured that if you have a crafting profession capable of putting an enhancement on your own items, it's going to be better and/or cheaper than the alternative. And if you're an enchanter, for god's sake put intellect on your rings.
Best: Arcanum of Hyjal (60 int + 35 crit) The Guardians of Hyjal are our head enchant faction this time around, and once you are revered with them, they will gladly sell you this account-bound bundle of extra stats for 150 gold.
Alternative: There really isn't one here. Questing through Hyjal and a few dailies and/or dungeon runs while wearing the tabard will easily get you to revered,
and only one of your characters needs to be at revered to then purchase this enchant for everybody else. So you've got no real excuses for not having the best in this particular slot.
Edit: For now, at least, it appears that this enchant, while being account-bound, also requires revered with the Guardians of Hyjal to use, and makes items soulbound once it is applied, meaning that each character who wishes to use it will need to be revered. This makes zero sense, and I expect it to be fixed 17 patches down the road when Blizzard gets around to it. I can't imagine any scenario in which this was intended. Either the account-bound status will be removed, or the item will stop requiring revered to use. Thanks to everyone who pointed this out!
Best: Greater Inscription of Charged Lodestone (50 int + 25 haste) You'll need to be exalted with Therazane to snag this one. Once you're there, you need only shell out 75g and you're good to go.
Alternative: Lesser Inscription of Charged Lodestone (30 int + 20 haste) You can pick this up in the same place and shockingly, it isn't actually any cheaper. But the time-poor mage will notice that this enchant only requires honored with Therazane. You'll hit honored before you're even done with the faction's main quest chain, so this'll do until you're able to crank out exalted.
Best: Greater Intellect (50 int) or Greater Critical Strike (65 crit) Here's a case where the best is actually cheaper than the alternative. 50 intellect is actually going to be more valuable than 65 crit in almost every situation and is far, far cheaper. If you're crazy, or have a disenchanter with stacks of Maelstrom Crystals in his bank and enough money that selling those Maelstrom Crystals at a ridiculous markup isn't attractive anymore, or just really need the crit for some reason, feel free to grab the 65 crit enchant. Also, I hate you.
Alternative: 50 int is the best enchant and also the cheapest. If PvP is your mage's focus, you may want to go ahead and put the incredibly cheap Greater Spell Piercing enchant.
Best: Peerless Stats (20 to all stats) As ever, there simply aren't a lot of good options out there for mages when it comes to dress enchants. This one at least gives us an extra 20 intellect. But at what cost? At what cost?
At the cost of 3 Maelstrom Crystals and 3 Heavenly Shards, that's what.
Alternative: Mighty Stats (15 to all stats) or Greater Resilience (40 resilience) So let's spend just a moment weighing cost versus benefit here. Maelstrom Crystals are going for between 1k and 1.5k gold on my server, depending on the day. The three Heavenly Shards will cost you somewhere in the neighborhood of 100 gold a pop. So for the prestige of having the best in slot enchant and a whopping 5 extra intellect, you're going to be shelling out something around 5 grand for this enchant in today's market. Take a 5 intellect hit and you're spending like 40 gold for two Lesser Celestial Essences. To recap:
We're weighing 5 intellect versus approximately 4960 gold. Frankly, if your guild leader yells at you for not having the best-in-slot enchant for your cloak, he's an ass, and you can tell him I said so.
The PvP option here is the ridiculously cheap Greater Resilience, and it's a no-brainer.
Best: Greater Critical Strike (65 crit) or Greater Speed (65 haste) These are fairly equal in terms of ridiculous costs, so take whichever you feel you need most. But if you aren't hit capped ...
Alternative: Precision (50 hit) ... take this one. It's far cheaper, and until you're hit-capped, the hit is far more valuable to you than either the haste or crit. I'd even look into taking the hit from somewhere else through reforging or gemming to make this enchant worthwhile. It's that much more cost-effective.
Best: Greater Mastery (65 mastery)
Alternative: Speed (50 haste) or Exceptional Spellpower (28 spellpower) The haste is far cheaper than the mastery at a smaller stat budget, but the old Wrath enchant is actually still viable. I'd probably still go with the haste here, but the 28 straight spellpower might work similarly well for your build and spec. Plug it into a DPS calculator and see what happens.
Only: Ebonsteel Belt Buckle (1 extra gem slot) This is your only option here, because the Wrath version doesn't work on the better Cataclysm items
Best: Powerful Enchanted Spellthread (95 int + 80 stam) This is by far the best option, but it'll cost you a piece of Dreamcloth, which can be extremely pricey. You're better off offering sexual favors to the least smelly tailor you can find. Good luck with that. We're a smelly bunch.
Alternative: Enchanted Spellthread (55 int + 65 stam) Far cheaper, but you lose 40 intellect. This is one case where you really need to be springing for the better enchant. Unless your mage happens to actually be a tailor, in which case you're golden.
Best: This is debatable, but probably Lavawalker (minor run speed + 35 mastery) If you need the extra mobility, this is the best run speed enchant out there. If you don't care about run speed ...
Alternative: Mastery (50 mastery), Haste (50 haste), or Precision (50 hit) ... these are all far cheaper and provide better stat bonuses. Up to you really. It's difficult to quantify the value of extra run speed, but you may find it valuable enough in movement-heavy fights to warrant the loss of stats and extra cost.
Best: Power Torrent (500 int for12 seconds) This is pretty awesome but predictably expensive. If you have a nice weapon, spring for it.
Alternative: Hurricane (450 haste for 12 seconds) This is such a massive step down from Power Torrent, and still fairly pricey, you should really just save your pennies and get the better enchant.
Only: Superior Intellect (100 int) This is your only option, but holy crap is it a good one. This extra 100 intellect is so good, it absolutely has to be factored into any two-hand versus one-hand/off-hand conversation from this point on. I like staves, don't get me wrong, but when you can put an extra hundred intellect on your off-hand that you have no way to recoup when you choose a two-hander ... that's tough to ignore. Plus, it's not too expensive, so there's that.
Edit: As many of you have pointed out, this enchant is being reduced to 40 intellect once patch 4.0.6 drops, which is a much more reasonable number. Maybe staves aren't a thing of the past after all. Thanks to everybody who noticed this!
So there you have your list of enchants for mages. Let's put on our best outfits, add some enchanted thread to our trousers, and go kill some warlocks, shall we?
Every week, Arcane Brilliance teleports you inside the wonderful world of mages and then hurls a Fireball in your face. Check out our recent Cataclysm 101 guide for new mages or our mage Thanksgiving spectacular. Until next week, keep the mage-train a-rollin'.