Directions:

Slowmotion:
First beat the game using any of the three characters and the hidden level with Isildur. Then while playing, pause and hold L + R then press Y, B, A, X.

Infinite arrows/axes:
First beat the game using any of the three characters and the hidden level with Isildur. Then while playing, pause and hold L + R then press X, B, A, Y.

All upgrades:
First beat the game using any of the three characters and the hidden level with Isildur. Then while playing, pause and hold L + R then press Y, B, Y, B.

Invincibility:
First beat the game using any of the three characters and the hidden level with Isildur. Then while playing, pause and hold L + R then press Y, X, A, B.

Always devestating:
First beat the game using any of the three characters and the hidden level with Isildur. Then while playing, pause and hold L + R then press B, B, X, X.

Tiny enemies:
First beat the game using any of the three characters and the hidden level with Isildur. Then while playing, pause and hold L + R then press Y, Y, A, A.

Restore health:
While playing, pause and hold L + R then press Y, Down, A, Up.

Restore Ammunition:
While playing, pause and hold L + R then press A, Down, Y, Up.

Add 1000 experience points:
While playing, pause and hold L + R then press A, Down, Down, Down.

Level 2 skills:
While playing, pause and hold L + R then press B, Right, B, Right.

Level 4 skills:
While playing, pause and hold L + R then press Y, Up, Y, Up.

Level 6 skills:
While playing, pause and hold L + R then press X, Left, X, Left.

Level 8 skills:
While playing, pause and hold L + R then press A, A, Down, Down.

Unlock Isildur:
Beat the game with all three characters to unlock Isildur as a playable character.

Aragorn's Secret Level:
Beat Helm's Deep: Hornburg Courtyard and reach level 10 with Aragorn to unlock his secret level.

Gimli's Secret Level:
Beat Helm's Deep: Hornburg Courtyard and reach level 10 with Gimli to unlock his secret level.

Legolas' Secret Level:
Beat Helm's Deep: Hornburg Courtyard and reach level 10 with Legolas to unlock his secret level.

Unlock John Rhys-Davis interview:
Reach level 5 using Gimli.

Unlock Viggo Mortenson interview:
Reach level 5 using Aragorn.

Unlock Orlando Bloom interview:
Reach level 5 using Legolas.

Unlock Production Photos:
Beat Balin's Tomb to unlock Fellowship of the Ring photos and beat Plains of Rohan to unlock Rohan and Helm's Deep photos.