Pause the game, hold the left trigger + right trigger and press down, a, x, black, a. You can now enter the following:

 Disable Shellshock – Press X, Y, A, B, Left, Trigger, X.

Infinite Health – Press white, black, Y, white, Left trigger, left trigger.

Hide Hud – Press black, left trigger, black, right trigger, up, Y.

Kill Nemesis – Press right, left, right trigger, left trigger, X, Y.

Unlimited Ammo – Press, L, Y, B, up, A, A.