I've never been a big fan of telling jokes about the mental abilities of President Bush - I don't think it helps the situation- but I did like this one from Rambling with Roger :
Don Rumsfeld is giving George W Bush his daily briefing and tells
him that three Brazilian soldiers have been killed in Iraq.
George says "that's absolutely terrible", is lost for words,
and holds his head in his hands for several minutes.
His staff are amazed at the response, and the whole room stays silent.
Finally George lifts his head from the table and says "exactly how
many is a brazillion?"