FFI: Once on GBA
FFII: Once on GBA
FFIII: Only barely played a little of it on DS. I still need to get around to that one
FFIV: Once on DS, about 3/4 on the snes version on virtual console
FFV: Own but haven't played yet
FFVI: Once on PS1 version
FFVII: Once with gameshark and once just recently without cheating. Lots of times playing through the midgar section and nothing else though
FFVIII: More than I can count. I'd say at least 15 times maybe
FFIX: I think I've only beaten it once. I used to have a copy that froze during cutscenes so I don't think I beat any playthroughs on that one.
FFX: 3 or 4 times
FFX-2: 3 or 4 times
FFXII: Once
FFXIII: Once
FFXIII-2: Once
LR: Once

Crisis Core: 2 times
Crystal Chronicles: The Crystal Bearers: Once
Theatrhythm and Curtain Call: Once each, I guess.

I think that's all I've really beaten. I've played others, but I just never can seem to beat them. (The tactics games for example. I love the style of game and really enjoyed those, but I just can never beat any of those kinds of games for whatever reason.)