The Topsy-Turvy bus is touring the US to "dramatically depict America's upside down budget priorities." Art car artist Tom Kennedy and his crew built it by welding together two yellow buses, one upside down on top of the other right side-up. Ben (Ben & Jerry's) Cohen hatched the idea with designer Stefan Sagmeister. Much more on the project at Laughing Squid.
Link (Thanks, Jennifer Lum!)