From the map screen, input:

Code        Effect
----------------------  
unlockall - Unlocks all the maps for that difficulty.
relockall - Locks all the maps for that difficulty.

During the game, input:

Code            Effect
-----------------------
double        - Double all friendly armies.
half          - Havles all enemy armies.
empty         - Empty all enemy countries of armies.
booth         - Strengthen your enemies.
woohoo        - Ear candy.
explode       - Eye candy.
winmap        - Wins the currently playing game.
command-left  - Go to the previous map
command-right - Go to the next map.