Level Select

When you see the words "Press Start" at the Title screen, press C-UP seven times. 

                              See the President

During a game, press Z, C-UP, and C-DOWN at the same time and the launch a homing cluster.
The President will jump out if it hits. 

                               Alien Disruptor

Beat level 7 on Expert difficulty. 

                                View Chopper

At the Chopper Select screen, highlight (don't select) a chopper and then press L. This will take
you to a screen showing the chopper rotating. You can control the chopper's rotation using the
control stick.