Any of the Silent Hill soundtracks would be my choice. I can't really name a single song on any of them that jumps out at me, but Yamaoka's trip-hop/ambient/experimental work is amazing, and stands above most other video game music as actually listenable on its own.
In fact, that's one of the two ways I judge good video game music: whether or not you want to listen to it out of the context of whatever game it was in. A few other games jump out at me in that respect: Beyond Good & Evil, the Digital Devil Saga games, and Rez. The other way is whether the music adds to the overall atmosphere of the game, the honor of which would probably go to Super Mario 64, Donkey Kong Country, Eternal Darkness, and a few others I can't think of at the moment.
"'Casual games' are something the 'Game Industry' invented to explain away the Wii success instead of actually listening or looking at what Nintendo did. There is no 'casual strategy' from Nintendo. 'Accessible strategy', yes, but ‘casual gamers’ is just the 'Game Industry''s polite way of saying what they feel: 'retarded gamers'."
-Sean Malstrom
