Make a Card Appear With the Tap of a Finger

This trick will blow you off your feet, so prepare to be amazed.

Steps

Get 10 cards in your hand.
Tell a member of the audience to remove a card.
Then ask them to place the card back into the set of 10 anywhere.
Keep an eye on the position of the card that they returned.
Tell them to close their eyes while you remove the card, and put it on the bottom.
Tell them to hold out their hand, in a loose fist. Put the cards in between their fingers and tell them to hold the cards tightly, but not too tight.
Slap the cards out of their hand, but not too hard.
If you did it right, the card that they picked will be the only one left in their hand.

This method is if you have some prior knowledge of magic and sleight of hand.

Have the mark take a card from the deck. Have them replace the card and use a false shuffle or cut to bring the card to a position you know. You can do this by secretly maintaining a break with the pinky finger above the selected card and then cutting the cards at that break.
Select a number of cards from the deck with the pretense of "feeling the energy of the card" or something mystical like that. Take out the selected card as well as 5-10 random cards, put on a show of selecting them. That's what magic is anyway.
Keep the selected card on the bottom of the stack of cards. False cut or shuffle the cards, keeping the selected card on the bottom.
Stick the cards in the marks fist, as above. To make it easier, have the cards slightly uneven and spread out, sticking the bottom card in further than the rest.
Slap the cards, as before. Watch the mark flip over the only card in their hand, revealing their selected card. Congrats, you performed a miracle.

Try not to slap yourself or the other person.
If the cards are hit too softly, only some of the cards will fall from your hand.
Be careful or you can hit yourself pretty hard.
If the cards are hit too hard, all of them will fall from your hand.