Quite by accident I "found" these new cheat codes in Twilight; I have not tested them in Dark Avatar or Dread Lords.
They are not listed on the GalCiv Wiki.
To enable "cheat mode" add the cheat parameter to your shortcut
Should look like this "C:\Program Files\Stardock Games\GalCiv2\Twilight\GC2TwilightOfTheArnor.exe" cheat
Shift + T= Summons 4 Arnorian ships (One Small, Medium, Large, and Huge hull- all w/ weapons and defenses) Will NOT add to military rating.
Shift + L= Auto Defeat
Shift + W= Auto Victory
Ctrl + Shift + G= Save current map (will bring up a dialogue screen for you to name and write a description. Wil be saved in My Games/Twilight/CustomMaps-this is a great one for you modders out there)
I didn't find anymore new ones, though there are a few duplicates (Ctrl+shift+Q will clone a ship, but so will Ctrl+C)