Arms Warriors (Yes, arms has always been good but fury used to be pretty OP.)
Any healer of any class
Warlocks have gotten a MAJOR boost.
And here are the nerfs:
Druids who were previously feral may no longer cat form a bg and tank a dungeon, you now are forced into choosing one or switching specs whenever you perform something. (Not much of a nerf but it sure doesn't benefit druids.)
And that's all I can think of right now.
If you know any other spec/class that has either been boosted or nerfed with 5.0.4, put it in a reply.