Well, that's entirely more reasonable than I usually expect when I say "what". Carry on!
seriously, though, a few suggestions:
Deus Ex - you can find many of the songs on Youtube. The game used the MOD file support of the Unreal Engine to have high-quality music at a small size with multiple tracks per file (like an area theme, the theme for that area when you're in combat, the theme when you're having a conversation, various transitional cues, etc) - in fact, the music was largely composed by Alexander Brandon, who together wtih Michiel van den Bos brought a lot of mod scene composing quality to not just Deus Ex but also Unreal, the original Unreal Tournament and some other PC classics. Unfortunately, the file format means that clean rips of the game are hard to come by. There's a partial soundtrack, but it was part of a limited edition (that you should admittedly own anyway, given how great the game is). Go ahead and download this, it's worth it.
Sadly, Brandon chose to go for a vastly more ambient style in Deus Ex 2 - the soundtrack was freely released, but other than the rearrangement of the main theme, I don't really think it has much to offer. Like the game itself, it's decent but is a pale shadow of it's predecessor.
Beyond Good and Evil - definitely seconding this one, as it has some truly beautiful music and extremely playful pieces that totally transcend what I usually expect from a Ubisoft game (although it is Ancel game, hmm). I should note that about a dozen or so of those tracks are actually medleys of thematically related songs which are distinct in the game's file structure, and there's about another half-dozen miscellaneous songs missing (most aren't really notable compared to what's already there). Sadly, I haven't seen any comprehensive rips that do anything nice like loop files or try and clean up the audio a bit.
Diablo series - Tristram theme, 'nuff said. Pity the composer went to join another company. :\
Ultima IX - listen to some pieces on Youtube....some very nice orchestral songs. They can be a bit repetitive, though.
When I think of PC music, I still think of DOS games with OPL synth. That's not a bad thing.
feel free to name some. I'm still marveling over what SoundTeMP did with Ys II Special...up until then, I always thought of the AdLib as "that old soundcard whose ass Creative kicked".