Under the Apple Tree and Moonlight Wandering are both very good. SOLDIER Battle, the Anxious Heart, and for some reason the song for the desert missions all go very well. Also, The World's Enemy is a pretty cool remix of One-Winged Angel. It's the most different of all the versions, but more than that it's very eclectic and chaotic which is really cool and pretty appropriate for when Sephiroth flies off the handle.
Lastly, I've gushed on this before, but Fulfilled Desire is probably the best credit roll in the history of credit rolls.