Cheats
Press ENTER and input the following codes for the decribed effects: (Unverified)

X marks the spot ... Reveals map
Medium Rare Please ... Stocks 10000 food
Give me liberty or give me coin ... Stocks 10000 coin
Nova & Orion ... Stocks 10000 XP
<censored> ... Stocks 10000 wood
A recent study indicated that 100% of herdables are obese ... All animals on map are fattened
Speed always wins ... Building rate doubled
Sooo Good ... Random saying when killed by infantry
This is too hard ... Clears current map in single player
tuck tuck tuck ... Stocks monster truck in retail version

 

Hack: Card Hack (Skirmish Mode)
Note: This involves altering a critical game file. Back up your files before you alter your FAT.

Locate the sp_NameOfCity_homcity.xml file in your \...\Age of Empires 3\savegame\ directory. Edit or open the file using Notepad or a similar text editor. In the file, search for the text similar to the string <activetech_name> and you should find a list of all the cards available for the game.

Place the technology card you want in between the <cards> and </cards> section and you should be able to play any of the cards you want. Save the XML file and boot the game. Note that normal game restrictions of having only eleven cards is still in effect.