IX had the best soundtrack, theres so many tracks I love on this game.
My favorites would have to be:

Terra
Bran Bal
You Are Not Alone
Feel My Blade
Battle Music
Freya's Theme
Gizamaluke Groto
Melodies of Life
Dark Messenger
Black Mage Village
Oeilvert
Ipsens Castle
Crystal World
The track that plays after you get the four mirrors....can't remember the name, its a fast upbeat version of Ipsens castle.

Theres more but, sadly as always, I can never remember them.