Well one's that have already been mentioned, obviously portal's ending ditty. L4D2 has some good 'shooting zombies to rock' stuff in the concert finale. Also ME, especially 2 had some really powerful bits of music, especially some of the mournful pieces. Also the radio on Fallout 3 had some songs which just fitted perfectly badly with the whole setting of the game if that makes sense.
Ones that haven't been mentioned.
Well, Jeff Waynes War of the Worlds, for obvious reasons (a computer game based on an album in many ways, that's how good the album was!). That may not really count though...
Also, KOTOR, the music that plays when you've got the launcher for the second game up before you actually load the game, that's some of the best music EVER, regardless of source in my opinion. (it's the second one and about 30 seconds long, have a quick listen)
Ones that haven't been mentioned.
Well, Jeff Waynes War of the Worlds, for obvious reasons (a computer game based on an album in many ways, that's how good the album was!). That may not really count though...
Also, KOTOR, the music that plays when you've got the launcher for the second game up before you actually load the game, that's some of the best music EVER, regardless of source in my opinion. (it's the second one and about 30 seconds long, have a quick listen)