Rebel Assault

At the LucasArts logo at the begining of the game, move the joystick up and then press fire, then down and fire, left and fire, and right and fire. If done correctly you'll here a phone ringing and a voice say "LucasArts". Once activated you can skip any level by pressing 1-9 goes to the respectove level. a-h goes to thre resta of the chapter(a goes to 10, b goes to 11, etc)

You can also repair your ship by pressing + on the keypad or skip the next level by pressing Esc.