For extra items and money, go to the items screen, hold R2 and L2, and then press SQUARE, SQUARE, SQUARE, UP, LEFT, DOWN, RIGHT.
On the title screen, press UP, DOWN, RIGHT, LEFT, X, X, X.
NOTE: You need two controllers (the right controller needs to be at least an Analog Controller) to do this cheat.
Pause (START) on the left controller and on the right controller, press L1, R3, R1, L3, RIGHT, SQUARE, UP, SQUARE, L2, LEFT, SQUARE, DOWN, R2. The game will unpause and you may control the nearest enemy using the right controller when your character is near enough in Story Mode.
To regain all health, pause the game and press UP, DOWN, RIGHT, LEFT, SQUARE, SQUARE, SQUARE.
To display the score, pause while playing and enter RIGHT, RIGHT, LEFT, LEFT on the right controller.
You can also add points artificially by this same method, except you need to hold L1 + R1 while pressing RIGHT, RIGHT, LEFT, LEFT.
While playing, pause and hold L1 + L2. Now press UP, UP, DOWN, DOWN, release the L buttons, press SQUARE, SQUARE, R1, R2.
On the item selection screen, hold all the shoulder buttons and press SQUARE, SQUARE, SQUARE, UP, LEFT, DOWN, RIGHT, SQUARE, UP, RIGHT, DOWN, LEFT. Note item slots are limited to six, but the item stock is now unlimited!
To unlock all characters, go to the title screen. Then press L1, R2, L2, R1, RIGHT, LEFT, L3, R3.
To unlock all items, go to the Items screen, hold R1+L1, then press UP, SQUARE, SQUARE, LEFT, SQUARE, SQUARE, DOWN, SQUARE, SQUARE, RIGHT, SQUARE, SQUARE.
To unlock all layouts, go to the Mission Select screen. Then press R3, L3, R2, L2, R1, L1.
To unlock all missions, go to the Mission Select screen. Then press L1, R1, L2, R2, RIGHT, SQUARE, L3, R3.
At the mission select screen for multi-player, press L1, R1, L2, R2, RIGHT, SQUARE, L3, R3.
To unlock the Bonus Stage, go to the title screen, then press L1, UP, R1, DOWN, L2, RIGHT, R2, LEFT.
On the title screen, hold L1 + R2 press DOWN, SQUARE, UP, SQUARE, RIGHT, SQUARE, LEFT, SQUARE. The choice will be listed OPTIONS -> AUDIO -> LANGUAGE -> B-SIDE.