Pong

At the Zone Selection screen, pause gameplay and press any of the following:
L1,R1,L1,R1 = Unlock 1st Level
L2,R2,L2,R2 = Unlock 2nd Level
L1+R1+L2+R2 = Unlock 3rd Level, secret power-ups, and 3 classic black and white Pong versions.

 