Okami. O-freaking-kami. I've been listening to the CD for the past two years and playing the songs on the piano.
Below that, Tetrisphere, Donkey Kong Country. and Medal of Honor: Frontline had really good ones, too.
Okami
To lavish praise upon this title, the assumption of a common plateau between player and game must be made. I won't open my unworthy mouth.