Shirt.woot.com hold a weekly shirt designing competition. Each week, a new concept is given to the public and designers all over the world are allowed to participate, and give their interpretation of the concept. Below are some of the designs I have submitted for the competition.
Entry links: http://shirt.woot.com/Derby/Entry.aspx?id=43186, http://shirt.woot.com/Derby/Entry.aspx?id=43924