I know I've raved about the music of Wrath of the Lich King in Beta, but generally, the music from other Blizzard games have been pretty topnotch. So while the Wrath soundtrack probably won't be out for a while -- it'll likely be included in the Collector's Edition -- you can head on over to the iTunes music store to pick up soundtracks from past Blizzard games such as Diablo, StarCraft, and of course, several albums from the Warcraft universe.
Most of the albums available were included in past Collector's Editions of Blizzard games, such as the original soundtracks of World of Warcraft and The Burning Crusade, and even the Warcraft III: Reign of Chaos soundtrack. One of the coolest soundtracks, I think, is the Taverns of Azeroth collection by new age composer David Arkenstone. I've been a fan of Arkenstone since his days at Narada, and it was a very pleasant surprise for me to learn he was doing music for World of Warcraft. If you enjoy the music of the World of Warcraft -- and other Blizzard games, you might want to check out the iTunes music store. As a bonus, you can even download the Diablo III Overture by Russell Brower for free.