Effect: The spectator is given the cards, which they may shuffle as much as they want. While the magician's back is turned, the spectator looks at the top card, and replaces it back on the top. The spectator is asked to place as many cards as the top card (King is 13, Queen is 12 and so on..) from the bottom to the top (still behind the magician's back). The magician turns around and takes the deck and finds the card!
This works based on a mathematical principle. All the magician does is start with the second card from the top, and counts mentally as one, two, and so on, going down through the deck. The spectator's card will be at the same number as the card value that matches the magician's count! There are better methods of revealing the result, however.
To the Reader: For this trick to work you have to know the number that the spectator has counted. To do this you can simply tell them to count out loud