This is a simple trick too, but use a little care when you handle the cards. Spread a normal deck of cards face-up on the table. Ask someone to point to any card they want.
Pull their chosen card from the spread deck and drop it on the bottom card. Pick up the deck and give it a couple of cuts. Now spread the deck, face down, and your friends see there is just one card with a different color back. You lift that card out and turn it over - that's right, it is their chosen card!