The Neverhood. By far. By too far to measure with our primitive Earth measuring devices. It kicks the excrement out of any game music ever devised. Having Terry Taylor mumble incoherently into the mike as he bangs out bluesy dixie land riffs on his accoustic while you wander about the final area is pure brilliance.
http://www.phileasphogg.net/reviews/terryt..._neverhood.html An article on the subject... too bad the soundtrack has been sold out for years now, along with the game.
http://mapmf.pmfst.hr/~marbel/music.html found a single mp3, the credits theme.
EDIT: Nevermind, check these out:
http://www.sfu.ca/~rfarahbo/home/theneverhood/TNMP3.htm Background music #2 is incredible, and a perfect example of the type of auditory treats found in the game. Also, be sure to check out Sound Effects record number 32. "Freeway sound from 20 miles away..... a Mime and his audience..... dead insect.... a swarm of dead insects..... tree falling in woods..."