On all these cheats you MUST pause and be holding the L and R buttons the whole time.
Aragorn: Up, B, Y, A, Give Aragorn 1,000 Experience Points Y, B, B, Y, Replenish Aragorn's Arrows Up, B, Y, Down, Aqcuire four upgrades immediately, when leveled up high enough. Upgrades: Dark Deliverance, Shield Cleaver, Lightning Strike, and Swift Justice.
Legolas's Gimli's and Sam's cheats can be used more then once.
Legolas, Gimli, and Sam: A, Y, Up, A, Give Legolas 1,000 experience. X, X, Y, A, Give Gimli 1,000 EP T, A, Down, A, Give Sam 1,000 EP
Gandalf: X, Y, Up, Down, Give Gandalf 1,000 EP Y, Up, B, A, Bring Gandalf to level 4
Unlock Frodo: Y, X, X, X, Unlocks Frodo for use. Y, Up, Down, X, Brings Frodo up to level 2
Secret Characters: Frodo Merry Pippin Faramir
You have to have beaten The Cracks of Doom to get, Merry, Pippin, and Faramir.