All Characters Unlocked:
At the main menu press L2, R2, L2, R2, Up, Right, Down, Left, L1, R1.
Alternate Sound Set:
At the main menu press L1, R1, L2, R2, L1, R1, L2, R2.
Change Ball Shape:
Press L2 + R1 + Triangle when the swing meter is on screen. Use left and right on the d-pad to change the shape of the ball.
Left Handed Players:
For a left-handed player, hold SELECT + L2 while selecting your character and then press X.