Like most of us, I've switched around professions several times on my main character.
My first combination of professions on my Warlock was Skinning + Leatherworking. I didn't know what I was doing when I first started playing, so I just grabbed those.
Once I hit 70, I grabbed Jewelcrafting in place of Leatherworking and Alchemy in place of Skinning.
Throughout 70, I dropped max Alchemy for Herbalism (Which I maxed out), then dropped for Mining (Maxed).
Once WoTLK went live, I dropped Mining for Inscriptioning (Maxed), and, just recently, dropped it and grabbed tailoring.
Warlock: 375 Skinning + 375 Leatherworking > 375 Jewelcrafting + 375 Alchemy > 375 Jewelcrafting + 375 Herbalism > 375 Jewelcrafting + 375 Mining > 450 Jewelcrafting + 450 Inscriptioning > 450 Jewelcrafting + 425 Tailoring.
How about you all out there? Any of you swap around professions as much as me? lol