Unlock Everything
When playing, head for the controller set-up menu while paused and input the following:

All comics: ... LEFT, LEFT, RIGHT, LEFT, UP, LEFT, LEFT, DOWN.
All characters ... RIGHT, DOWN, RIGHT, DOWN, LEFT, LUP, LEFT, RIGHT.
All landmarks ... UP, RIGHT, DOWN, LEFT, DOWN, UP, RIGHT, LEFT.
All concept art ... DOWN, DOWN, DOWN, UP, DOWN, UP, LEFT, LEFT.