Hold out the index finger on your non-dominant hand. Balance an index card on your finger and then place a penny on top of the card (so that the penny is essentially sitting on your finger - there's just an index card between them).
Use your dominant hand to flick the index card out of the way. If things are balanced properly and you flick the card quickly enough so that inertia overcomes friction, you'll be left with a penny balanced on your finger.
