Big Cars
At the main menu, press and hold L2+R2, then press Up, Up, Up, Square, Square, Square.
Extra Cash Bonus
During the race position your vehicle on a power-up icon that always reappears as cash. The icon will keep reappearing and you will keep picking it up. Just be sure to finish the lap before time runs out or you will lose all the cash that you picked up. This also works with icons that always reappear as nitros.
Infinite nitros
Pause the game, hold R1 + R2 and press Down, Down, Down, Circle, Circle, Circle.
Infinite weapons
Pause the game, hold R1 + R2 and press Left, Up, Right, Down, Square, Triangle, Circle, X.
Invincibility
At the main menu hold R2+R1 and press Up, Left, Right, Down, Triangle, Circle, X.
Small Cars
At the main menu, press and hold L1+R1, then press Down, Down, Down, Circle, Circle.
Voodoo Car
At the main menu, press and hold L2 then press Left, Right, Down, Up, Square, Circle, X, Triangle.