Received a five dollar bill today with a URL stamped on it. "Track this bill's journey www.whereswilly.com". For those of you that are curious to see how money travels around the world, this is the site for you.
Update: Sept 5th, 2006
At the request by the Where's Willy staff and after over 500 replies to this post, I have been asked to shut down the replies. Apparently my popularity is hurting them.