In the options menu hold L1+R1 and enter the following:

Triangle, Triangle, Square, Square - Blow up vehicles in one hit
Square, Square, Square, Square - Faster cars
Triangle, Triangle, Triangle, Triangle - Fastest cars
Triangle, X, Triangle, X - Infinite car health
Square, Square, Square, Triangle - Press horn to do a huge leap in your car
Circle, Circle, Circle, X - More camera angles
Circle, X, Circle, Triangle - Grid mode
X, Circle, X, Circle - All reward Cars
X, Square, Square, Triangle - Credits
Triangle, Triangle, Circle, Square - Speedometer display
Circle, Circle, Triangle, Square - Red Brick Car
Triangle, Circle, Triangle, Circle - Tripping mode