There is a lot of great music.
Planescape: Torment
In my opinion, a fantastic score. I'm not sure about its appeal to other people, but the exotic stile owns me.
The music is also available at Interplay's site, with the sigil battle theme here:
http://www.interplay.com/interact/downloadlist.asp?Dltype=1
Unreal Tournament
Cool mixture of rock/metal/etc.
Play with
http://www.modplug.com
Deus Ex
Awesome soundtrack, especially considering that its hours worth of music in all (aprox. 28 individual pieces, with individual conversation/battle/walking/etc. subpieces).
Can be listened to with the same program as above.
Monkey Island Series
(most fan sites have the music)
Grim Fandango
Mexican style!
(fansites for music)
Medal of Honor: Allied Assault/Call of Duty
Heroic pieces, in .mp3 format.
Morrowind/Dungeon Siege/Star Wars: Kotor
All by Jeremy Soule, all great.
Half-Life
Very atmospheric, with some cool pieces (adrenaline guitar)
Grand Theft Auto/Vice City
First of which has the tracks on the play CD.
Mafia
Etc.
[This message has been edited by KnobZ (edited February 16, 2004).]