Kimahri's pretty damn useful for the early Steal/Lv. 3 keysphere/Mighty Guard stuff mentioned in this thread, but it's also worth mentioning that, pre-Celestial Weapons, he also has a bunch of *really* nice (and varied) weapon drops from chests. Much of his stuff is fairly standard attack+X% and Piercing, so basically Auron's weapon drops, but he also gets some pretty great magic-user weapons IIRC.
That said, if they ever actually remake FFX, I hope they either make Blue Magic way more offensively powerful like the other limits, or at least make Jump an actual turn-delayed classic Jump command that you can use to avoid big AoE attacks.