First shuffle the deck. Then have somebody randomly pick three cards out of the deck. Have him (or her) look at the cards and memorize one of them, not paying any attention to the other two. The other two just act as fodder...

Deal two cards onto the table face down. Have him put one of his three cards face down on top of those two. Deal four cards on top. Have him put another of his cards face down on those. Deal four more cards on top. Have him put his final card on top. Deal two more cards. So the order should be: 1, 2, [card], 1, 2, 3, 4, [card], 1, 2, 3, 4, [card], 1, 2

From the stack of cards you just made, pull five cards off the top and fan them in front of the person. Ask if he sees his card. If not, discard these, show him the next five cards and ask again. If he again says no, use the remaining five cards.

Now you should have five cards with his card in the middle (hopefully he won't catch on to the fact that it's obvious it's the middle card. He probably won't). Take the full deck that you set aside earlier. Cut off half the deck. Put the first of the five cards onto the half-deck you are holding, but not square with the other cards. Place it so that about half the card sticks up beyond the rest at the end. Take the next of the five cards and put it on the deck so that it is square with the deck (not with the card that sticks up). Put the next card on the deck so that it sticks up like the first card, the next card square with the deck, and the last so that it sticks up. So it should go: up, square, up, square, up. Make sure the three up cards stick out about halfway beyond the rest of the cards.

Put the other half of the cut deck on top of the five cards you just arranged, squared with the half-deck below.

Now the tricky part. Hold the deck in your hand by the sides so that the three projecting cards point down. Hit the end of the deck on the table--not too hard, but not too light--so that two cards pop out of the other end. Flip the deck around and hit the two cards on the table. The card that remains sticking out is the card that they picked. This is more of a math trick, but it does look very impressive.