To unlock the following, insert the passwords on the main menu (where campaigns can be selected, et cetera:

    G1 Jazz Skin - Left, Up, Down, Down, Left, Up, Right
    G1 Megatron Skin - Down, Left, Left, Down, Right, Right, Up
    G1 Optimus Prime Skin - Down, Right, Left, Up, Down, Down, Left
    G1 Starscream Skin - Right, Down, Left, Left, Down, Up, Up
    No Vehicles, Military, or Police - Right, Left, Right, Left, Right, Left, Right
    Robovision Optimus Prime Skin - Down, Down, Up, Up, Right, Right, Right
    Unlock All Missions - Down, Up, Left, Right, Right, Right, Up, Down
    Unlock both Cybertron Missions - Right, Up, Up, Down, Right, Left, Left
    Unlock Unlimited Ammo - Up, Down, Left, Right, Up, Up, Down
    Unlock Unlimited Health (Invincibility) - Left, Left, Up, Left, Right, Down