YouTube - Toki No Hourousha
It's Terra's theme in Final Fantasy VI. I really love that song, especially with lyrics. But when I played the game, I couldn't leave the world map for a long time, just because I wanted to listen to the song. I didn't enjoy the map anymore when I was in the World of Ruin, but... ah well.
And, of course:
YouTube - #1 - Aria Di Mezzo Carattere (Opera Theme) - Final Fantasy 6
Rawr. *_* I love that song. There is also a version with lyrics, but I also like the version of the game itself. And I liked the fact that you had to learn the scene by heart. :>
All in all, FFVI had the best music for me. But there were quite a few songs I liked in other games as well. :> (Like Cid's Theme in FFVII or the Theme of the Empire in FFXII :>)