Gregory showed me this one at the Dutch Magic Convention in may 2002. Grip a card between the index and the thumb at about the middle of the long side. Then you flick with your middle finger the card strait up or a bit with an angle to boomerang the card.
An alternative which is even better, is the flick up flight. Pick the card with the thumb and index finger off centre to the right. (see picture). Now flick it with your middle finger and it will fly to the left and you can catch it after a beautiful flight.