Anything by Nobuo Uematsu. Seriously.
Also liking the Shadow of the Colossus soundtrack, and other soundtracks like that.
Other than that mostly games with an oldschool appeal to the music. I love C64/Amiga-music, and 8-bit music almost as much. Some games on the DS, like Phoenix Wright and the Castlevania titles are good on that aspect, with the Castlevanias actually using some of the melodies of older games in the series, a wonderful homage to those great games. I'm sure the new Megaman will have great music too.