This custom silver ink, developed by materials researchers at the University of Illinois, Urbana-Champaign, allows you to draw working circuits out on paper. It's extremely cool, and the video shows you step-by-step how they make it. Bonus: This ink provides an actual reason to use cursive.
Video Link (Via Aaron Rowe)
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.