Okay, here's a list of games with a pretty good soundtracks:
Strike Suit Zero. Seriously, it was composed by the same guy, who made Homeworld soundtrack.
Tribes: Vengeance. Highly underrated game with pretty good music.
Edge / Edge reloaded. Good electronic music. For a fun casual arcade, a port from mobile, it has some sweet tunes.
Spartan Strike. Simply incredible job for another port from them phones. If you like styles of both new and old generations of halo music - this game has tracks for ya.
X: Reborn. Bad game, but the soundtrack makes it good. Sometimes even epic.
Freelancer. It is impossible to imagine this game with other music. The atmosphere... I simply cannot describe it.
Xonotic. For arena shooter, it has a pretty good music. Nothing special, just good.
King's Bounty (Armored Princess in particular). when I heard it for the first time, I just lost my jaw. Simply incredible.
Space Rangers 2: A War Apart. This game has A LOT of good (and different!) music. Once again, it really makes the atmosphere of the game.
Unreal: Return to Na Pali. It is impossible not to fall in love with this soundtrac, just impossible. Or, should I say, unreal?
And the last one...
Shut up and jam Gaiden. Omg, the music in this game is fantastic!
That's all I could remember.
P.s. Happy Birthday Room Ross!