Generic
Arcane/Frost build for raiding in MC and BWL.
Points in Magic Absorption and Improved Counterspell can be moved around for stuff like Magic Attunement or Improved Arcane Missiles.
One mage in MC/BWL will be running
Winter Chill spec to provide debuff on boss for rest of mages. He may ditch PoM in Arcane and go for Ice Barrier in Frost since he's that deep in Frost anyway, but it's more of personal preference.
For raids where mobs do not have fire immunities you can go
Fire/Arcane, just be sure to take those 3 points in Frost for Elemental Precision.
QFT.
I actually made a pre-raid BIS guide when I was mage CL, but I don't have access to that list atm, and I don't really feel like redoing it. Also now that I think about it, it had items such as Bloodvine and Rockfury, pieces that wont be available at the start. Ah to heck with it here goes. I am going to be lazy tho!
Head: Spellweavers Turban - Drakkisath(UBRS)
Neck: Diana's Pearl Necklace - Cannnonmaster Willy (Strat Living)
Shoulders: Boreal Mantle - Eh can't remember who drops it tbh, think it's in BRD, check it urself^^
Cloak: Amplifying Cloak - Dire Maul / Random Green with frost dmg.
Chest: Robe of the Archmage - You need to be a tailor, pattern drops in LBRS, but can be bought on AH as well. / If you're not a tailor(you ought to be!) Freezing Lich's Robe is next best option - drops in Scholo off Raz.
Bracers: Sublime Wristguards - Dire Maul
Gloves: Hands of Power - LBRS
Belt: Ban'thok Sash - BRD
Legs: Skyshroud Leggings - LBRS
Boots: Omnicast Boots - BRD
Rings
on Mauricio's Band of Domination- Scholomance(Gandling) + Freezing Band(world drop)/Maiden's Circle(world drop)
Trinkets: Briarwood Reed(Jed in UBRS) + Eye of the Beast(Questline, ends in UBRS)
Weapon:Lord Valthalak's Staff of Command - LBRS (At least until AV comes out)
Wand: Bonecreeper Stylus - Scholomance(Gandling) / Ritssyn's Wand of Bad Mojo - Strat dead(Baron)
Note that this list doesn't contain items that can be obtained via PvP.
Note also that this was done mostly from memory so some things may be wrong.
Note that I only included the items I find the best, not items that are almost as good.