From The Real Secrets of Magic, by David Stone. It's a very easy effect that hits hard on spectators. I added a little convincer at the end, what do you think?
http://www.youtube.com/watch?v=FhN0VQWr1HA&list=UU9Sg54ZNa2qMmMlDvTJcqoA&index=1&feature=plcp