Oooh... I just love them! Be it listen to them or play them! I own all of them and love them all, but I like these ones the most:
-Troian Beauty (IV)
-Battle with Gilgamesh (V)
-Mambo de Chocobo (V)
-The decisive Battle (VI)
-Tina (VI)
-Main Theme (VII)
-Aeris' Theme (VII)
-Those who fight (VII)
-Blue Fields (VIII)
-Eyes on Me (VIII)
-Eternal Harvest (IX)
-You're not alone! (IX)
-At Zanarkand (X)
-Decisive Battle (X)
-Eternity ~ Memory of Lightwaves (X-2)