At the main menu hold L+R then enter one of the cheats below:
Effect : Code
Anti-Gravity: Up, Up, Left, Right, Up, Up, Up, Up, L3
Extra Life: Y, A, X, B, Up, Left, Down, Right, L3
Level Select: Down, Up, Left, Left, Up, Right, Right, Right, L3
Magnet Pegs: Y, Up, Y, Up, Y, Down, Y, Down, L3
Shield: Left, Right, X, B, Y, A, Up, Down, L3
Super Spin: Left, Up, Right, Down, Down, Right, Up, Left, L3
Unlock All Bikes: Down, Up, Right, Right, Right, Right, Right, Right, L3
Unlock All Characters: Left, Up, Down, Right, Up, Down, Up, Right, L3
Unlock All Movies: Right, Up, Down, Down, Up, Right, Down, Down, L3
Unlock All Songs: Right, Right, Right, Right, Right, Right, Up, Down, L3
Note: L3 = Push in left thumbstick