The following 2 codes are the only ones authorized by InterAct

Infinite Gil            8009d260ffff
Quick Level Gain        8009d7d8ffff

The rest of these codes are unauthorized and may not work. Use at your own risk.

Start the Game With W-Summon                    8009D0C4 0014 
Start the game with Master Summon               8009D9A0 005A 
Save Anywhere                                   8009D2A6 0000 
Limit Break every turn for first character      800F5E6A 00FF 
Limit Break every turn for second character     800F5E9C 00FF 
Limit Break every turn for third character      800F5Ed2 00FF 
Always get 65535 EXP points after battle        8009D7D8 FFFF 
Always get 50000 AP Point after battle          8009D7DC C350 
No Random Battles                               8007173C 0000  
No Random Battles on the World Map              8011627C 0000 
All characters to level 99 (use after battle)   801FFDD6 0100  
                                                8009D7DA 0100 
Max out Materia in first slot                   8009CE62 0100 
Cloud's HP 9999                                 8009D85C 270F  
                                                8009D85E 270F
Automatic Replenish Slot 1                      800F840C 270F 
Always have 9999 HP for Tifa                    8009DC9C 270F 
                                                8009DC9E 270F
Auto Replenish Slot 2                           800F8474 270F 
Always have 9999 HP for Barrett                 8009E0DC 270F   
                                                8009E0DE 270F
Auto Replenish Slot 3                           800F84DC 270F  
Cloud has all possible Limit Attack             8009C75A 0FFF 
Tifa has all possible Limit Attack              8009C862 0FFF 
Barrett has all possible Limit Attack           8009C7DE 0FFF 
Yuffie has all possible Limit Attack            8009C9EE 0FFF 
Red XIII has all possible Limit Attack          8009C96A 0FFF 
Aerith has all possible Limit Attack            8009C8E6 0FFF 
Cid has all possible Limit Attack               8009CB7A 0FFF 
Vincent has all possible Limit Attack           8009CAF6 0FFF 
Cait Sith has all possible Limit Attack         8009CA72 0FFF 
Have 9999 Gold Points at the Golden Saucer      8009D3D2 270F 
Have 50000 Battle Points at the Golden Saucer   8009D3D8 C350 
Infinite life for Cloud                         8009C764 270F 
Infinite MP for Cloud                           8009C768 03E7 
No Monsters                                     80070674 0000 
                                                801160C0 0000
Turn any growing Chocobo into a Gold Chocobo    8009BC4E 0400