At the main menu select "Classified Files" and press X. Then enter the following codes 

Effect     -     Code 

Invincibility - TEAMBUDDIES
Unlimited Ammo - BLASTRADIUS
Level Select - KINGSLEY
Bonus Level 1 - KREUZLER
Bonus Level 2 - SHEARER 
Bonus Level 3 - UBERDOOPER 

Mini-Game:
Use the "Bonus Level 3" code then hold up on the left analog stick and press Square, Triangle, Circle, Triangle , Square, Circle when the bonus level intro sequence begins. Press X to stop the intro sequence. Press X to move in the mini game, and Triangle to change views.