The Svengali deck is a fantastic utility deck, which allows a specific card to be forced upon your spectator.

A sample effect:
A small picture frame covered with a cloth is placed on the table. You explain that it's a photo of your Uncle Monty, who was a mentalist. You shuffle a deck of cards, and fan them out to show all faces are different. You ask the spectator to select a card and keep it well hidden from anyone in the room.
The spectator now for the first time shows their card... and the picture of Uncle Monty is revealed to be showing him holding the same card!

The Svengali deck can be riffled and shown as a normal deck.