Cruis'n USA 

To get secret vehicles: Go to the car selection screen. Choose the muscle car, the la bamba, or the devastator then press and hold UP,DOWN, and LEFT C.

To make the police car or the bus flash thier lights or sirens: Take 1st in a race and put in your initials. go down to the bottom of the screen and hold left for around 30 seconds. You will see a head come by on the conveyor belt. Now that the cheat is activated just push BRAKE, BRAKE, and then hold GAS.

To get a boost: Make the head appear as above. Then in a race push BRAKE, BRAKE, BRAKE, GAS, BRAKE, GAS. This only seems to work once per checkpoint.

To directly access some stages: Go to the course selection screen. Next hold down the following codes: Golden Gate Park : LEFT C, BOTTOM C, L Indiana : TOP C, RIGHT C, L San Francisco : RIGHT C, BOTTOM C, L