I recently got my hands on some 'Electric Paint', from a company called Bare Conductive. Basically, it allows you to build electronic circuits quickly, by using the surface of the paper (or any substrate), as the circuit board, and the paint becoming the wires. I've been noodling around with it to create different applications, from simple desktop lights, through to more complex sensing ideas. It's pretty cool stuff, and you can find out more about it here:
http://www.bareconductive.com