The cheat is "power overwhelming". Its the most fun while playing against protoss because there supposed to be superior. You can attack a nexus with one guy and destroy it while the protoss attack you and there protoss dark archon can't even ruffle your armour or mind control you. (does not work in multiplayer =()
The cheat is "game over man" and it makes you instanly fail current objectives. It gets you less perks and you get a lecture frome the boss of your current tribe. (terran, protoss or zerg) depends who you are playing the level for. (does not work in multiplayer).
To instantly win your current level type in "There is no cow level" you will instantly win. This is a cool way to win if you want to get to the good mission's. There is one catch though you cannot use it in multi-player.