Silent Hills 1, 2 and 3. 4, 5 and Origins had a few good tracks each but overall the music (which is a huge part of the reason I got into Silent Hill - demo trailer OPM 99) was a letdown.
As a second choice, and I hate to admit it, but the Halo soundtracks are quite beautiful and work as pieces all by themselves. Mirror's Edge accomplishes this as well ... especially that end of demo trailer piece, beautiful.