Hmm
As a Nine Inch Nails fan I have to admit the Quake soundtrack was incredibly atmospheric, even though I didn't like the game half as much as Doom.
I liked the Unreal soundtrack as well, it was the first time I encountered music that got more tense when approaching an enemy and it worked awfully well somehow.
And offcourse the Monkey Island (1&2) tunes, the evergreens in the adventrure gaming industry.
And I will never forget the tune of Alley Cat, no matter how crappy it sounds.
Oh yeah, Jazz Jackrabbit 1 & 2 have got some great catchy music as well
I've got taste I have