Full Ammunition:
Pause gameplay, then hold R1 + R2 and press Select. A female voice will say "Impressive" to confirm . Note: This code must be re-entered after loading or upon entering new areas.

Unlimited Ammunition:
Press Start to pause game play, then hold L1 + L2 + R1 + R2 + Square. A female voice will say "Impressive" when done correctly. Resume game play and your ammunition will read 999.

All Weapons:
Pause game play, then hold L1 + L2 + L3+ R1 + R2 and press Select. A female voice will say "Impressive" to confirm . Press Left or Right to cycle through the weapons. Note: This code must be re-entered after loading or upon entering new areas.

Autotarget Mode:
Pause game play, then hold L1 + L2 and press Select. A female voice will say "Impressive" to confirm . A small text message will appear in the upper left corner of the screen the game is resumed that displays the status of this cheat. Note: This code must be re-entered after loading or upon entering new areas.

Refill Armor to 100:
Pause game play, then hold L1 + R1 and press Select. A female voice will say "Impressive" to confirm. Note: This code must be re-entered after loading or upon entering new areas.

Undying Mode (999 health):
Pause game play, then hold L1 + L2 + R1 + R2 and press Select. A female voice will say "Impressive" to confirm. A small text message will appear in the upper left corner of the screen the game is resumed that displays the status of this cheat. You can still take damage with this code. Note: This code must be re-entered after loading or upon entering new areas.

God Mode:
Pause the game and press R1 + L1 + R2 + L2 + R3 + Select A female voice will say "Impressive" to confirm. A small text message will appear in the upper left corner of the screen the game is resumed that displays the status of this cheat. You can still take damage with this code. Note: This code must be re-entered after loading or upon entering new areas.

Thanks to Revolution reader Chris!