Invincibility
Pause the game (as sarge) and press Square, O, L1, L1 + L2. You will now be invincible.
Submitted by Mega_Legend. 

Unlimited Weapons
Pause the game (as sarge) and press Square, O, R1, L1, R1 + R2. You will now have unlimited weapons.
Submitted by Mega_Legend. 

Level Select
At the main menu, press Square, O, R1, L1, L1 + R1 for a level select.
Submitted by Seth. 

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