Here at WoW Insider, we've been on a beginners' class guide kick. But after taking the time to put together my shadow priest leveling guide (and after reading the warlock leveling guide written by my less talented coworker), I realized that we didn't have any kind of leveling guides for professions. Time to fix that! After all, you need professions to make money.
But first, the most important question: What professions should your character choose? The best answer is always going to be "whatever appeals to you most" -- but if you're a magic-using, cloth-wearing class, I'd recommend you at least take a look at tailoring. By leveling it, you get access to Lightweave Embroidery, one of the best level 85 buffs in the game for casters.
Of course, you can level tailoring on any character, and a lot of the craftables you make can be sold at a profit. But if that character can't use the buffs from the profession, you're missing one the key benefits to max leveling a profession.