This classic probably doesn't need any introduction.  A clear disc and an opaque disc are shown, both blank.  They are placed together and the solid one can be seen through the transparent one.  They are now placed in a volunteer's open palm.

A spectator picks a card from a deck.  The person holding the discs is instructing to gently shake them.  As they do a card VISIBLY appears and matches the selection!

VERY EASY TO PERFORM and looks like miracle!