Enter the following at the Main Menu:

Mirror tracks		Z, R, Z, Z, R, Z, Z
Night Racing		C-Up, C-Up, C-Down, C-Down, C-Left, C-Right, C-Left, C-Right
Stealth mode		C-Left, Z, Z, C-Up, C-Left, R, C-Down, C-Up 
TowJam car		    C-Up, C-Down, Z, R, C-Left, C-Right, C-Up, C-Down 
Unlimited turbos	C-Right, Z, C-Up, C-Down, R, C-Left, Z, C-Right
Wire frame mode		C-Up, Z, C-Down, C-Left, C-Up, Z, C-Down, C-Left

All cars & tracks:
Enter the password WYVW2LVDW VTXWWVWWWF.

Hints

Hidden Cars:
Some Bonus cars are hidden under a jump or cliff. eg. On the Dawn Encounter track. I am sure all of you have jumped over the UFO and gone through the tunnel. There is a cliff in that tunnel. Go over it and drive backwards to get the Lakester car. This rule also works on the Snake River Mine track.

Hidden Cars

Sol-aire CX4:
In Command Center, near the cranes, crash through the 2nd grate on the right and follow the tunnel. You should find the prize.

Rock Buster:
In Road to Rustwell, go in between the bridge and the ramp in the town. go behind the shack and break through the wall.

Slideout:
In Cold Fusion, after the red and black loop-d-loop, crash through the boxes on the right. When in the cave, back-up into the boxes.

Jet Threat:
Use Gulch Stepper car. In Cold Fusion, right at the start, back up a bit and crash through the snowballs and contnue down the tunnel. Crash through the left wall acrosss from the 3rd light. Smash into the ice.

Super Van:
In Helicrash shoot up the U-turn, grab the car of steel power-up, smash through the wall and grab the car.

Formula 5000:
Use small car. In Snake river mine, go to the cave with the mine cart. When the coast is clear, turn left onto the mine cart track.

Thanks to Revolution readers Wild49er, Anonymous, Eric Churchill, Stephen and Buckaroo!