In this short video, Steve Spangler shows you how to levitate thin plastic objects using
a magic wand the power of static electricity. You can read all the details on his science blog; here's a snippet explaining the most important part (spoiler alert -- if you want to think through the science puzzle on your own, don't read this italicized bit before watching the video):
Rubbing the towel against the balloon and the plastic band transfers a negative charge to both objects. The band floats above the balloon because the like charges repel one another. If you really want to impress someone, just tell them that it's a demonstration of "electrostatic propulsion and the repulsion of like charge." That should do it.
(Via The Kid Should See This.)