Outcast, especially the city theme. Very original composition and absolutely tear-jerking sound from the Hungarian Radio Choir. Ways ahead of it's time as well. The music sounds almost too much like a modern John Williams st.
Hitman 2 and Hitman: Blood Money. It's funny how much Kyd has improved with every game he has scored. This guy can do practically any kind of genre and style.
Thief series, thanks to a certain Brosius. Incredibly solid and fitting sound for games released years ago. Still have some of the best atmosphere of all time.
I found Rune to have a great mix of rock, viking choirs and ambient. If you can find the soundtrack, Galbadia Hotel should have it, listen to the bonus tracks. Some of the best ambient I've heard there. You'll crap your pants.
Soule, Klepacki, Hoenig, Ruskay, Brown(ospierro pero!) and the sound guy for HL 2.