Master Cheat:
Enter LONGO at the 'Codes' menu to unlock all bonus stuff and missions.

Invincibility:
Enter SOLID at the 'Codes' menu.

Remove the HUD, Keep the Radar:
Enter CONVISTA at the 'Codes' menu. you will fly without that cruddy viewscreen that covers up the edge of the screen

Mara Jade's Headhunter ship:
Enter HUNT at the 'Codes' menu. It has homing missiles and a strong dual laser.

Alternate camera angles:
Enter DARON at the 'Codes' menu..

Thanks to Revolution readers BOB, Warman602, and Tyler Satterfield!