There's heaps of guitar tabs around for most Final Fantasies. I recently learnt this one:
4shared.com - online file sharing and storage - download Memories of Lightwave.mp3

Sight of Spira is my current project, but it is quite hard. The tab can be found here:
http://www.freewebs.com/stamen47/spira%20unplugged.pdf

There's also To Zanarkand, which isn't that hard to play:
http://www.freewebs.com/stamen47/zanarkand.pdf

Edit: For some reason you guys, and the guy that made the tab, call it "Spira Unplugged" when on the soundtrack it's called "Sight of Spira".