X by James Conti

A card is selected and returned to the deck. Next, the magician introduces the "X" card within the deck: a card with a big, bold "X" drawn onto its back. When its face is revealed, unfortunately it doesn't match the spectator's selection. But with just a flick, the "X" on the back of the card magically changes into the value and suit of their selected card! 

This is super visual and happens in a blink of an eye! And it looks great - very magical!