The Deck That Shuffles Itself (Gimmick and Online Instructions) by Dominique Duvivier. He pretends to take the deck (in fact, the deck stays on the table and he acts as if he had the deck in his hands), put it on the table in front of him, cut it in half, turn one pile face-up and shuffle both parts with a riffle shuffle, square the deck, take it, and put it back where the real deck was.
eBay