Play The Fanghorn Forest Level:
Beat the game with all the characters.

Play The Helm's Deep Level:
Beat the game with any character.

Play The Moria Level:
Beat the game with any character.

Play The Weathertop Level:
Beat the game with all artifacts collected.

Play as Smeagol:
Beat the game with any two characters to play as Smeagol in the Helm's Deep or Moria levels.

Play as Sam:
Link to a Gamecube and play the GCN version of ROTK. Sam will be unlocked and playable in multiplayer mode as well as on bonus maps.

Duplicate Items:
If one player gives another player an item in multiplayer mode, and the receiving player saves the game but the giving player does not, then the giver will still have the item when he or she restarts.

Free runes with Frodo:
After you defeat Shelob, Frodo will get kidnapped. You have to free him with Sam. After you have freed him get out the building and go down the stairs. You will find a rune each time you enter this area.

Thanks to Revolution readers Henry and Edo van der Weide!