Beat the game. Then while playing press pause, hold R1 + R2 + L1 + L2 and enter the cheat codes.
Invincibility:
Square, Circle, Square, Down.
Perfect mode:
Circle, Up, Triangle, Down.
All attack upgrades:
Down, Up, Triangle, Square.
Full health:
Square, Square, Circle, Circle.
Unlimited missile weapons:
Square, Square, Up, Circle.
Always devastating:
Triangle, Down, Triangle, Up.
Target indicator:
Up, Circle, Down, Square.
Unlock all interviews:
X, Square, X, Up.
Unlock Faramir:
X, X, Triangle, Triangle.
Unlock Frodo:
Triangle, Circle, Circle, Circle.
Unlock Merry:
X, Down, Down, X.
Unlock Pippin:
Triangle, Circle, Square, Down.
Co-op codes:
Share experience:
Down, X, X, X.
Share health:
Triangle, Up, Square, Square.
Unlimited respawns:
Circle, Square, Up, Circle.
Aragorn codes:
Three-hit combo:
Square, Down, Circle, Up.
Four-hit combo:
Up, Square, Triangle, Down.
All special abilities:
Down, Circle, Triangle, Triangle.
1,000 experience points:
Up, Square, Triangle, X.
Level 8 skills:
Up, Square, Triangle, Up.
Restore missiles:
Triangle, Square, Square, Triangle.
Gandalf codes:
Three-hit combo:
Down, X, Triangle, Down.
Four-hit combo:
Down, Triangle, Up, Circle.
All special abilities:
Up, Down, Triangle, Circle.
1,000 experience points:
Circle, Triangle, Up, Down.
Level 8 skills:
Circle, Square, Down, Down.
Restore missiles:
Triangle, Down, X, Square.
Gimli codes:
Four-hit combo:
Triangle, Square, Up, X.
1,000 experience points:
Circle, Circle, Triangle, X.
Level 8 skills:
X, Circle, Down, Square.
Restore missiles:
Circle, Circle, Circle, X.
Legolas codes:
Three-hit combo:
Triangle, Triangle, Triangle, Down.
Four-hit combo:
X, Circle, Triangle, Square.
All special abilities:
Triangle, Circle, X, Circle.
1,000 experience points:
X, Triangle, Up, X.
Level 8 skills:
Square, Up, Up, Down.
Restore missiles:
Triangle, Triangle, Triangle, Down.
Merry codes:
Four-hit combo:
Triangle, X, Square, Square.
1,000 experience points:
Down, Down, Square, X.
Level 8 skills:
Down, Triangle, X, Square.
Restore missiles:
Square, Circle, Circle, Triangle.
Pippin codes:
Four-hit combo:
X, X, Down, Circle.
1,000 experience points:
Triangle, X, Square, X.
Level 8 skills:
Square, Up, Up, Circle.
Restore missiles:
Up, Circle, Down, Square.
Sam codes:
Four-hit combo:
Up, Down, Triangle, Triangle.
1,000 experience points:
Triangle, X, Down, X.
Level 8 skills:
Circle, Circle, Triangle, Triangle.
Restore missiles:
X, X, Circle, X.
Faramir codes:
Four-hit combo:
X, Square, Up, X.
1,000 experience points:
Square, Triangle, Up, Square.
Level 8 skills:
Circle, Down, Down, Down.
Restore missiles:
Triangle, Up, X, X.
Frodo codes:
Four-hit combo:
Down, Square, Down, Circle.
1,000 experience points:
Down, Triangle, Up, Down.
Level 8 skills:
Circle, Circle, Down, Down.
Restore missiles:
Triangle, Triangle, Triangle, Circle.
Defeat shielded orcs:
To defeat shielded orcs use the X button to get underneath the orc and then you can knock him to the ground and do some serious damage.
(supplied by: Bigsistercassy)
Pellenor Fields Strategy Guide:
Try to concentrate all your power on the easterlings, as this is the way to advance through. Once you're on the hill, have Legolas\Aragorn (if you're playing single-player and you have Gimli then just use the catapults) shoot the mumakil until it explodes. When the second comes go between the catapult on the far left and the middle catapult, to go down the ramp. Don't fight the easterlings and orcs, just move across to the other ramp. Once on the ramp use the same strategy as before to kill the mumakil. Once done with that hurry down the ramp to Merry and Eowyn. Don't stop to fight. Once you're there then you just use your ranged weapon to take out the witch king (Legolas would be nice here).
(supplied by: Lizardman)