End Bonuses
Beat the game to unlock the following:
Palantir of Saruman
Billy Boyd interview
Dom Monaghan interview
Andy Serkis interview
David Menham interview
Planatir of Sauron (You must have Sam, Gandalf, and one of the 3 main characters - Aragorn, Legolas, Gimli - at level 10 or above.)

Unlock Four-Hit Combo For Aragorn
Pause the game and hold both triggers. Then press UP, B, Y, DOWN.

Unlock Gandalf's Level 4 Abilities
Press START and hold the L and R buttons. Then press Y, UP, B, A. This should unlock them. You will know it worked if you hear a metal "clank" sound

Unlock Secret Characters
Beat the game to unlock Pippen, Merry and Faramir.

Hint: Shoot Faster
Get out your ranged weapon, press and hold Y, R, and A at the same time, and then you should fire faster