Melodies of Life, You're Not Anone, Ambush Attack, Mage vs Mage were among my favorite tracks in FF9 OST and FF9 OST Plus.

Many people here seem to like Kuja's themes. I think Dark Messenger was my favorite version of Kuja's theme (it plays when you (SPOILER)fight him in the Memoria and it has pieces of his melody), but Immoral Melody is also great.