Here are cheats i remember for X:
lightning dodges (need to be consecutive)
Butterfly timer for catching them
Chocobo timer for races (cant gain time, stay under 0:00)
Blitzball (score, exp, all abilities unlocked)
AP multiplier and/or Max Sphere Level
All creatures captured
Instant Kill, Infinite Hp & Mp, and usual FF combat stuff
All overdrive modes unlocked (takes 1000 turns for some, too long)
Instant/full overdrives,Max Gil, item cheats - already in-game
Here are some cheats for X-2:
Max Gil
Ap Muliplier
Max & all items (no game or side quest breaking items this game that i remember)
Blitzball stuff again
Usual FF combat cheats
I know i am missing alot of possible ones but these are the ones i can recall for both that are important, especially the lightning, butterfly and chocobo ones for X. The AP stuff for both games is a major help because the sphere grid in X and Dress Sphere in X-2 require lots of work to complete, and people may not want to sink in hundreds of hours again on X/X-2 to max them out again.
Also f1 - f5 is already being used for the ingame cheats already.