Invincibility
Y, Y, X, RB, X, LB

Replenish Health
LB, LB, RB, X, RB, Y

Team Invincible
X, X, Y, RB, Y, LB

Unlimited Ammo
RB, RB, LB, X, LB, Y

Enter the following code at the Mission Select menu:

Unlock Level
Y, RB, Y, RB, X