Pause during play, then enter the following codes:

Big ball:
L1, L2, L1, L2, Up, Right, Down, Left.

Big bodies:
Up, Down, Left, Right, L1, L2, R2, R1.

No bodies:
R1, R2, R1, R2, Up, Down, Left, Right.

Big heads:
Up, Left, Down, Right, Up, Right, Down, Left.

Small heads:
Up, Down, Up, Down, R1, R1, L1, L1.

Fast players:
Left, Right, Right , Left, L1, R1, R1, L1.

Slow players:
Left, Left, Right, Right, R2, R2, L2, L2.

Programmer names:
R1, R2, Right, Right, Left, Left, L2, L1.

Thanks to Revolution readers Minkus and Martin Brodeur!