verydemotivational.com (http://verydemotivational.com/) has a lot of very funny fake motivational posters. Here are my three favorites.
(http://verydemotivational.com/wp-content/uploads/2009/11/129035151383770462.jpg)
(http://verydemotivational.com/wp-content/uploads/2009/11/129034757224804830.jpg)
(http://verydemotivational.com/wp-content/uploads/2009/11/129034750514093934.jpg)
Check out the site for larger versions.