Level select:
Pause the game, hold Square and press Up, Down, Left, Right, Right, Right, Down, Left.
Level select alternative:
pause the game and press Right, Square, Triangle, Square, Triangle, R1, L1, R1, L1, Triangle, Down.

Level skip:
Pause the game, hold Square and press Right, Left, Up, Up, Up, Right, Left, Left.

Infinite lives:
Pause the game, hold Square and press Down, Down, Up, Down, Right, Down, Up, Up.

Infinite lives alternative:
pause the game and press Right, Square, Triangle, Square, Triangle, X.

All extras and bonus levels:
Pause the game, hold Square and press Right, Up, Up, Down, Right, Down, Right.

All characters:
Pause the game, hold Square and press Left, Right, Left, Left, Left, Up, Left, Left.

Temporary invincibility:
Pause the game, hold Square and press Left, Left, Up, Left, Down, Right, Right, Right.

Turn coins into Mad Garibs:
Pause the game, hold Square and press Right, Left, Right, Left, Up, Up, Left, Right.

Control main menu screen:
Go to the main menu, press Circle to say "Ribbit" or Square to lick and eat the fish and bugs.

Level secret:
Get all the gold coins on a level to unlock a secret for that level.