The Lord Of The Rings: The Return Of The King Codes -

Fanghorn level:
Successfully complete the game with all the characters.

Helm's Deep level:
Kill at least 2,000 enemies as any single character (not a total between several characters).

Moria level:
Successfully complete the game as any character.

Weathertop level:
Successfully complete the game with all artifacts collected.

Play as Smeagol:
Successfully complete the game with at least two characters to unlock Smeagol in the Helm's Deep or Moria levels. He can also be selected in multi-player mode.

Play as Sam:
Use a link cable to connect to a Gamecube and play its version of The Lord Of The Rings: The Return Of The King. Sam will be unlocked in multi-player or bonus maps as a selectable character.

Ancient Artifacts:
Use a link cable to connect to a Gamecube and play its version of The Lord Of The Rings: The Return Of The King. Ancient Artifacts that can be sold for extra gems can now be found.

Duplicate items:
In multi-player mode, have one player give an item to the other. Then, have the receiving player save the while the sender does not. Next, have both players quit. If done correctly, both players should now have all the items.