Cheat Codes:
On the main start menu, enter the following:

Unlock All Drag Tracks - Right, Square, Left, R1, Square, L1, L2, R2
Unlock All Drift Tracks - Left, Left, Left, Left, Right, R2, R1, L2
Unlock All Circuit Tracks - Down, R1, R1, R1, R2, R2, R2, Square
Unlock All Sprint Tracks - Up, R2, R2, R2, R1, Down, Down, Down
Unlimited Nitro - X, CIRCLE, TRIANGLE, TRIANGLE, X, X, CIRCLE
Get Free Parts - X, X, TRIANGLE, X
Unlock Drift Physics in All Modes - R1, UP, UP, UP, DOWN, DOWN, DOWN, L1

Extra 150 Style Points:
At the beginning of a race, tap your NOS button (if you have any equipped) to do a NOS purge, and you will get an extra 150 style points.

Points for 360 in Drift:
When you are in drift mode you can get some extra points for doing doughnuts. Hold one direction and the handbrake and gas and let go of the handbrake after a second. You'll just sit there and do doughnuts. This won't get you massive points but it's something.

Unlock Samantha's Car:
Unlock all of the Vinyls by getting enough Style Points. Fill it up one more time to get her car.