I think Fire was my most common non-Cure spell, though Gravity and Aero would be a close second and third, especially in the last world and during the final boss.. and Hade's Cup/ Sephiroth battle, though I recommend you don't use it against Ice Titan. As for KH2, what this thread was about, that's kind of pointless, but unless you leave Reflectaga out to, it's that. Besides, Reflect and Cure, I rarely use any magic in KH2, except maybe Magnet, when I'm working on leveling up the drive forms (especially Final Form). I also used it to make the "Imma chargin' mai lazor, Imma firin' mai lazor" segments of the final boss battle faster.
Though.. I do tend to use either fire or thunder for a better than normal looking ending to the final battle and once used it to finish off Saix before he went into Berserk mode. (and once to stall him a little once the bar was full)