Tailoring isn't the best, there are no best professions really, anyway ... tailoring will be very nice for mages come The Burning Crusade as you'll be able to craft your own Shadoweave or Spellfire cloth depending on whether you have Shadoweave Tailoring or Spellfire tailoring.
Those sets are epic quality cloth armorpieces availible only to tailors (as in, they're BoP) at level 70. A good choice. That and you'll be able to craft your own spellthreads (though as a Mage don't forget to take the right reputation for it (Aldor or Scryers, they switched recently).
Enchanting is also quite nice with the BoP Ring enchants (+damage, +4 all stats, etc.) that Enchanters can only apply to their own rings.
Or any of the money making professions like Herbalism (with or without Alchemy), Mining (with or without Jewelcrafting), Skinning, etc.