Casus by Michael Kociolek

A deck of cards is given to a spectator to shuffle, and she's asked to silently think of any number between 1 and 52. The performer then asks the spectator to freely select a card and remember it.

At no time during the effect does the performer know the spectator's number or the value of the chosen card. He briefly shuffles the deck, asks the spectator to hold out her hand, and places the face down deck on her palm. The spectator then deals cards, one by one face down, to her chosen number.

She then turns this card face up. It's her chosen card.

This effect is 100% impromptu. Any deck can be used.