Vigilante 8 

All vehicles 
Enter "GANGS_UNLOCKED" as a password. Note: This does not unlock the UFO.

"Y" the Alien 
Enter "GIMME_DA_ALIEN" as a password.

Super Dreamland 64 level 
Enter "DDDDDDDDDDDDDD" as a password. Alternatively, successfully complete all of "Y" the Alien's missions in "Quest" mode to unlock the Nintendo 64 exclusive bonus level. -From: xuliming@bellsouth.net

All vehicles and levels 
Enter "JTBT7CFD1LRMGW" as a password. -From: kingcodebra@yahoo.com

Level select 
Enter "LEVEL_SHORTCUT" as a password.

Invincibility 
Enter "LIVING_FOREVER" as a password.

Missile power-up 
Enter "MISSILE_ATTACK" as a password.

Quick firing weapons 
Enter "FIRE_NO_LIMITS" as a password.

Ultra-high resolution mode 
Enter "MAX_RESOLUTION" as a password.

Same vehicle in multi-player mode 
Enter "MIX_MATCH_CARS" as a password.

Low gravity 
Enter "A_MOON_GETAWAY" as a password.

No enemies 
Enter "POPULATION_OUT" as a password.

Slow motion mode 
Enter "GO_REALLY_SLOW" as a password.

Expert mode 
Enter "I_AM_TOUGH_GUY" as a password.

View ending sequences 
Enter "LONG_SLIDESHOW" as a password.

Play as Dave 
Successfully complete "Quest" mode with Chassey Blue and Slick Clyde.

Play as Convoy 
Successfully complete "Quest" mode with Sheila and John Torque.

Play as Molo 
Successfully complete "Quest" mode with Loki and Houston 3.

Play as Sid Burn 
Successfully complete "Quest" mode with Boogie and Beezwax.

Play as "Y" the Alien 
Successfully complete "Quest" mode with all characters.

Special weapons 
Enter the following actions while playing a game to active the special attack of the indicated weapon. Note: The required weapon must be in the inventory, but does not need to be currently active.

Interceptor Missiles (Halo Decoy), uses 2 missiles 
Press Up(2), Down then shoot the machine gun to cause your opponent's homing missiles or special attacks to follow your missiles instead of your vehicle.

Interceptor Missiles (Turbo), uses 2 missiles 
Press Up(3) then shoot the machine gun to speed up for a few seconds.

Bull's Eye Rockets (Stampede), uses 1-5 rockets 
Press Up, Down, Up then shoot the machine gun to rapidly fire multiple non-homing rockets.

Bull's Eye Rockets (Boost Rocket), uses 2 rockets 
Press Up, Down, Up, then shoot the machine gun. If an opponent is hit, he or she is taken for a sky ride.

Sky Hammer Mortar (Turtle Turnover), uses 2 shells 
Press Down(3) then shoot the machine gun to flip your opponents' vehicles.

Sky Hammer Mortar (Crater Maker), uses 5 shells 
Press Down(2), Up, then shoot the machine gun to drop a mega bomb that will leave a crater.

Bruiser Cannon (Cow Puncher), uses 2 shells 
Press Down, Up, Down then shoot the machine gun to punch opponent vehicles back.

Bruiser Cannon (Scatter Blast), uses six shells 
Press Down, Up(2), then shoot the machine gun to shoot six cannon shells simultaneously.

Roadkill Mines (Cactus Patch), uses 1-6 mines 
Press Left, Right, Up then shoot the machine gun to rapidly deploy a group of mines.

Roadkill Mines (Magnetic Mine), uses two mines 
Press Left, Right, Down, then shoot the machine gun to drop a mine that will attract nearby cars.