All Weapons:
To get all weapons you have to go to the main screen and press L1, R2, L2, R1, X.

Invincibility:
During the game pause and press the following, L2, L2, R1, R2,R1, L2 and u will have invincibility.

Gold Cheat:
To get gold you must beat the game on hard. Winning gold will give you infinite ammo, all weapons and all the rest of the multiplayer codes you receive when you win silver and bronze.

Silver Cheat:
To enable Silver Cheat, finish the game in Medium difficulty. This will open 2 more bars in
multiplayer mode: Game Speed and Blast Force. Plus it will unlock the multiplayer cheats you get for winning bronze.

Bronze Cheats:
Beat the game on the easy difficulty. This will give you two options for multiplayer mode: Weapons Stay and One hit kill.