Get TowJam Car:
At the main menu press C-Up, C-Down, Z, R, C-Left, C-Right, C-Up, C-Down

Unlimited Turbos:
At the main menu press C-Right, Z, C-Up, C-Down, R, C-Left, Z, C-Right

Nightime Racing:
At the main menu press C-Up, C-Up, C-Down, C-Down, C-Left, C-Right, C-Left, C-Right

Stealth Mode:
At the main menu press C-Left, Z, Z, C-Up, C-Left, R, C-Down, C-Up

Wire frame Display:
At the main menu press C-Up, Z, C-Down, C-Left, C-Up, Z, C-Down, C-Left

Mirrored Tracks:
At the main menu press Z, R, Z, Z, R, Z, Z

Bonus cars and tracks:
Enter "99T8DTY8VD D7BDDDDDD2" as a password. Alternatively, win the Hot Wheels Cup.

Additional bonus cars:
Enter "9PTNPTFN6P NMQPPNPPPL" as a password.

All Cars and Tracks:
When you start the game go down to "sign in" then move over to "password". Then for all cars and tracks put in 1 of these 3 passwords: _WYVW2LVDW VTXWWVWWWF
_WYVVZCVDV VTXVVVVVVN
_WYZKZ1VDD OTX1TRGHSV

Mystery Cars:
On the "Test Track" when you get in the room with the three or four pillars(columns) after the first one, there is a panel on the right wall, that is discolored. Ram thrugh it and inside the tunnel, is a box shaped liked a car, that has ???'s all over it. Hit the box head on, and you'll recieve a new car.