Definitely most of the stuff Nobuo Uematsu does. The majority of the FF soundtracks kicked serious ass, but his best stuff is Chrono Cross. I have the entire soundtrack on mp3 and listen to it quite regularly, especially the main theme.
The old Lunar soundtracks are fun for some retro musical enjoyment, and it's hard to beat the minimalist fun of the original Metroid.
One of the cooler things about soundtracks is remixes of old favorites--one of the best sites to get remixes from is Overclocked Remix, at
http://remix.overclocked.org/index.php. Good stuff, if a bit too heavy on the techno/house remixes, and they have a very, VERY wide variety on what the in house mixmonkeys will jam with.