Enter these codes while the game is paused. A beep will confirm the code. To disable a code simply re-enter it. 

Any Object -- Down, Down, Up, Up, Right, Right, Left, Left 
Behind Car View -- Left, Right, Square, Circle, Left, Right, Square, Circle 
Big Bounces -- Square, Right, Right, Down, Up, Down, Left, Down, Down 
Double Speed -- Square, X, Circle, Square, Triangle, X, X, X, X 
Floating Objects -- Square, Triangle, Square, Square, Triangle, Square, Square, Triangle, X 
Slow CPU Cars -- Circle, Triangle, Square, X, Circle, Triangle, Square, X 

Debug Mode 

Pause the game and press Square, Up, Down, Down, Square, Circle, Circle, Triangle, X to enable Debug Mode. To use it, press any of the button sequences below while you're playing. 
Quit Race and Win -- Press Select + X. This doesn't work in time trials. 
Change Camera Angle -- Hold Select and press Up, Down, Left or Right. 
Change Camera Zoom -- Hold Select and press L2 or R2. 
Turn Player into Computer Drone -- Hold Select and press Square. 
Blow up all cars -- Hold X + Triangle + Circle + Square 

Easter Eggs 

Enter these codes on the Name Entry screen. You will hear a beep if you entered them correctly. 

3LIVES -- ? 
CONFETTI -- ? 
CATLIVES -- 9 lives in one-player mode 
GIMMEALL -- All tracks in multi-player game. 
NOTANKS -- Tanks cannot shoot. 
TANKS4ME -- Tanks can be used on all tracks except those with water. 
WINTERY -- Slippery roads. 

Turbo Start 

For a faster start, press the accelerator button during the second beep at the starting line.