(Highlighted words are not links; i'm too lazy to find all of these things.
)
The soundtrack of the
Halo series, particularly the first one,
Halo: Combat Evolved. The later games are pretty good too, but the first one will always be my favorite.
Although it's certainly not main reason i like the games, the
Borderlands series does have a handful of good tracks. Main ones that come to mind are Skag Gully and Caustic Caverns
I don't know if this really counts, but
Burnout 3: Takedown has a wonderful soundtrack. I was introduced to some of my favorite bands though said game.
Any
Oddworld game. Seriously, the music alone is worth giving them a look, not even mentioning the games themselves. (Disclaimer: I have only played
Munch's Odyssey and
Stranger's Wrath, so i can't speak for any of the others.)
And last but certainly not least, the soundtrack from a really old game that nobody has ever heard of.
Airforce Delta Storm. The game isn't fantastic, though it is very nostalgic for me (first console game i ever played). But the music is awesome. Might be the reason i still play it every now and then.