Oh man, I used to just loop the 4 seasonal soundtracks from Shogun on my PC while doing homework in college. There was another track from the Mongol expansion that I enjoyed too, don't remember the name of it.

The Mechwarrior 2 games (Original, Ghost Bear Legacy, and Mercs, ESP. Mercs) were also outstanding, I still have my original mp3s I ripped off of my game cds from years and years ago.

I kinda liked the Deus Ex soundtrack. The Hong Kong streets music was probably my fav... cheesy, but I liked it.

And the Fallout soundtrack, I found a good looping version of the Brotherhood of Steel compound background music. The air raid sirens were just great in that.

Secret of Mana. Dark Lich theme ftw.

Final Fantasy series have always had good music. Apparently many folks didn't like the game overall, but Final Fantasy Mystic Quest, the final boss theme was one I really enjoyed.

Need For Speed 5 soundtrack was good.

Diablo 2 soundtrack was also good. My friend made a few looping versions of some of the area themes so we could listen to that in college as well.

The Wipeout games have always had absolutely outstanding music, but that's really most of what the games were about IMO. XL and 3 are my two favs.

Will post more if I can think of them.