Note: You must have version 1.1 patch for the following codes to work. 

Mission Select:
Start a new game and enter your name as TheWorldIsYours, then double click on it
and then click scenario.

Cheat Mode:
Start a new game and enter your name as TheGalaxyIsYours, then double click on
it. Now enter the following during play:

Code                 Result 
M                    500 Command Points
SHIFT + M            500 Command Points and Order Any Unit 
CTRL  + W            Win the Mission 
CTRL  + 8            Show Active Units 
CTRL  + SHIFT + 8    Show All Units 
CTRL  + 9            Remove Fog of War 

Double Unit Carriers:
When a unit carrier explodes, remove the unit at the same time it explodes. If you
timed it right, that unit will have doubled.