Enter at the menu that has campaign and bonus features listed:

G1 Megatron
Down, Left, Left, Down, Right, Right, Up.

G1 Optimus Prime
Up, Up, Down, Down, Right, Right, Right.

Infinite Ammo
Up, Down, Left, Right, Up, Up, Down.

Jazz G1 skin
Left, Up, Down, Down, Left, Up, Right.

No vehicle's running on the street and no tank's/cop's attack
Right, Left, Right, Left, Right, Left, Right

Robovision Optimus Prime skin
Down, Down, Up, Up, Right, Right, Right

Starscream G1 skin
Right, Down, Left, Left, Down, Up, Up

Unlock All Mission
Down, Up, Left, Right, Right, Right, Up, Down

Unlocks Bonus Cybertron Autobot And Cybertron Decepticon Missions
Right, Up, Up, Down, Right, Left, Left.