Here are some cheats from the game. I will try and find more as they come out so keep checking back :)

Black Jack
First, complete the game. Once the credits finish and "The End" screen appears, press R2, L1, R2, R2, Up, X, Right, Circle, Down, Triangle, L2, R1, R2, L1, Square(2). If you entered the code correctly, you will hear a sound. Press Start to begin playing the black jack game

Skip FMV
When the FMV begins, quickly open the cover of your PSX, and then close it. The game is going to resume at the point where the FMV has just ended. And if  you are using PS2, just push the eject button to take the CD-Rom out and then push the button again to put it in

Moogle, Angry!?
Call out a moogle by pushing the square button on the worldmap. When you call up the moogle and let him go back without doing anything for many times, it will be talking in different ways. There are going to be 3 different lines when he is angry.

Zidane's "Reach Seven" Skill!
Zidane's "Reach Seven" skill is going to work when the single-digit of his HP is "7" . It is going  to cause a random damages of "7", "77", "777" and "7777". However, if the single-digit of his HP is not "7", then the damages it is going to cuase will always be "1".

Weird Guy
There is a weird looking guy who will appear in many places in the world of gaia, he will ask questions, and if you answered it correctly, you will get a lot of APs. In addition to this, once you answer all his 13 Questions correctly, you will get a memory ring!

Unlimited Money!
If you go back to Chocobo Paradise after visited all the beaches. you are going to get unlimited Dead Pepper. If you've finished our stock of Dead Pepper, we can refill from the Chocobo left of Fat Chocobo. But I've forgotten what button to press. He'll say that we can have his stock of Dead Pepper. It'll refill our Dead Pepper to 99. Now we can go and sell it and then Back to Chocobo Paradise. Refill then sell again. Keep repeating these steps and you are going to get Unlimited Money!