A lot of them are pretty good.
Teldrassil & Ashenvale
Hellfire Peninsula (awesome, the impact of that music and that completely different style zone the first few times around, probably a good part of the reason why I love questing through Outland)
Music that was in early tauren area, can't recall the name.
Oh yeah, Vortex Pinnacle (really different and fit the instance so well)
There's an area in Feralas that has the Cataclysm Nelf-music, that stuff is awesome too
OTOH I'm probably one of the only people who doesn't like the Grizzly Hills music. I get what they're trying to do but it just doesn't hit the mark for me.