Vigilante 8: Second Offense

Invincibility:
Enter ELBICNIVNI as a password. This is especially useful in quest mode.

All characters:
Enter LLA_KCOLNU as a password to unlock all characters.
Note: Their quests will not be completed.

All characters have maximum stats:
Enter LLA_DORTOH as a password.

Special attacks:

Interceptor Missiles
Attack 1: Up, Up, Down, Machine Gun
Attack 2: Up, Up, Up, Machine Gun
Attack 3: Up, Up, Right, Machine Gun

Bull's Eye Rockets
Attack 1: Up, Down, Down, Machine Gun
Attack 2: Up, Down, Up, Machine Gun
Attack 3: Up, Down, Right, Machine Gun

Sky Hammer Mortar
Attack 1: Down, Down, Down, Machine Gun
Attack 2: Down, Down, Up, Machine Gun
Attack 3: Down, Down, Right, Machine Gun

Brusier Cannon
Attack 1: Down, Up, Down, Machine Gun
Attack 2: Down, Up, Up, Machine Gun
Attack 3: Down, Up, Right, Machine Gun

Roadkill Mines
Attack 1: Left, Right, Down, Machine Gun
Attack 2: Left, Right, Up, Machine Gun
Attack 3: Right, Left, Right, Machine Gun

Brimstone Burner
Attack 1: Right, Left, Up, Machine Gun
Attack 2: Right, Left, Down, Machine Gun
Attack 3: Right, Left, Right, Machine Gun

Password screen:
Enter the options screen, select "Game Status"
then press L1 + R1.

Rapid fire mode:
Enter RAPID_FIRE as a password.

Solo play in arcade mode:
Enter HOME_ALONE as a password.

(Information from Cheat Machine)