This isn't quite a full list, but is such a cool Egg (and not really a cheat) that I hope it might be worth posting...

1 - Start the game, and choose to start from the beginning.

2 - After the opening "STAY LOW!", DON'T SHOOT ANYTHING. The aliens will continue shooting you and costing you energy and lives, IGNORE IT.

3 - The moment a member of your team (humans in blue uniforms) appears, shoot them. You lose a life, don't worry.

4 - Keep waiting - still not shooting anything. Soon there will be another team member who appears hiding behind a box - blow them away and lose another life. BUT YOU DON'T... in fact, now nothing will harm you until the next part of the egg. But still DON'T SHOOT ANYTHING.

5 - A helicopter will appear and shoot missiles at them. Ignore them all - they can't hurt you. (This is usually where anyone watching you play gets surprised.)

6 - Another team member runs past at the bottom of the screen. Shoot them. (Be warned, if you miss, your immunity is cancelled and you are playing the normal game with one life left.)

7 - The moment you shoot the team member, the section will end, and you'll be shown a text screen explaining that you're now playing an alien rebel. All your lives and energy will be returned to you. For the rest of the game, the backgrounds will be in random messed up colours and your score will be increased. Also, you get a unique symbol on the high score table.