Carbonite(mainly quest helper, but I like what it does to the map and it lets me see guildmates and friends regardledss of whether im in a group with them)
Lightheaded(Carbonite 'mod'. Links to wowhead or thottbot and lets you see the comments for quests. i.e.~ quest is being a bitch and in the comments you see you needed to grab this piece that the quest wasnt too clear about, all the while staying completely in game)
IceHUD(I LOVE that I can see my hp/ma and my targets hp/ma without looking away from the middle of the screen)
GearScore(b/c I want to see whos uberest around me
)
Xperl + Bartender(I could live without thses, but they are nice once you get them setup)
Cooldowns(BIG flashing numbers on your buttons = win vs all)
Titan panel(first addon Ive ever had and i consider it a part of the wow ui, lol)
Auctioneer(duh)
DeadlyBossMods(waaaaaaaaaay helpful for new places or tired raids)
Omen3(everyone needs this... period. Tanks need to know if the have enough agro, EVERYONE ELSE needs to know if they have too much. Dont be the annoying agro grabber, get this mod)
Recount(how much face am I melting?)
YourMama(who's yer daddy?)
YourFace(Ooooo, I said it... what?)