Unlock Hover Bike:
Get a "Great" rating on all of the missions.

Unlimited counter measures:
Pause the game and press Y, Y, Y, X, X, Z, Z.

Glass Car:
Pause the game and press Left, Right, Left, Right, Z, Z, R.

Zero Gravity:
Pause the game and press X, Z, X, Z, Up, Up, Up.

Cars Fly When Hit :
Pause the game and press Z, R, Z, R, Right, Right, Right.

Thanks to Revolution readers TroJax and ryukami75482!