At the main menu hold L and R triggers and press Left, Up, Down, A, Right, B, Start and enter any code below at the cheats menu:

SUPERMECH Invincibility
WEWILLWIN Get All Levels
WHERESMAX Get All models and awards
BACKSTABBER Get One shot kills
SNIPER Get One sniper shot kills
MULTIMAYHEM Unlock All multiplayer levels
FLIPSIDE Get Upside down mode
MISSMACROSS New paint schemes
MARSBASE Faster missile refresh
SPACEFOLD Fast gun pod refresh
MIRIYA Faster missile + gun pod refresh
CLEAR Cheat Codes Turned Off