I am no FF7 booster, but One Winged Angel was off the charts as far as boss music goes. It just had this very apocalyptic feel to it. Takes me back to college nights during summer vacation after my freshman year playing with the stereo cranked up... the insane bass of the KOTR summon blasting with OWA's just unstoppable evil vibe.

The only other Final Fantasy music I really liked (although X does have some good stuff) was the theme that played in FF6 as the opening credits played, with the mechs walking in the snow.