A spectator randomly picks a card from a deck. The magician hands the deck back and allows the spectator to shuffle and cut as many times as he wants. The magician takes the deck back and throws it against a nearby window. When all the cards fall down, one is stuck to the window. The spectator is shocked to realize it is his card, but gets even more shocked upon discovering the card is on the OTHER side of the window!
Stand outside of a building with access to a nearby window. Give your helper a deck of cards and instruct him to tape the duplicate of any chosen card to the window (in a way the tape cannot be seen).
Position yourself and your spectator so that you face the window, and they cannot see it.
Riffle through the deck and have her pick a card. Instruct her to hold it up so you cannot see it. Your assistant will see it and simultaneously tape the duplicate to the window.
Have her put the card back into the deck.
Hand the deck to her and have her shuffle as much as she wants. This will ensure you are not doing anything tricky.
Take the deck back and fling it at the window. When all the cards fall down, her chosen card will appear on the window.
To show that it is on the other side, ask her to go get the card. When she goes to grab it she will realize and flip out.
Do not perform until you have this down pat and your assistant, too. If the wrong card appears on the window, you run the risk of exposing how it's done.