Yep, Chris is right, it is called an Omni Deck. You can find these at Penguin for $11 or so. A great tool indeed.
I use it every day at the restaurant I work at. I do a two card selection routine, in which I force a card and have one freely selected. Then, I control the freely selected one to the top.
Then, I double lift, and pretend I messed up...etc. Make a joke about the card box, and place the top card (their selection) into the card box and tell them to shake the box. After they are done shaking the box I have them look inside. That is selection number one.
While they are shaking the box, I simply put the deck in my back pocket and switch it with an omni deck that has the forced card on top. I then say to. The other spectator after the first reaction is over "i didn't find yours yet though."
So I have them hold their hand out flat, place the omni there, (no spectator has ever felt the difference between an omni deck and a real feel of a bottom card/deck) and place their other hand on top.
I say "I am going to steal all the cards except for your selection...etc." A lot of buildup though!
Then do a steal-like gesture and say "it is done."
This is a very confusing moment for laymen because they can physically feel the deck and that you haven't taken anything.
I tell them to turn over the top card. As they see their card, they also notice that the deck is clear. I was right after all! Haha.
Honestly, this trick is remembered forever, and I hope one of you will use it, as I am already feeling bad about revealing it (it is my original creation).
I can truthfully say that no spectator has ever held the omni on their hands for longer than a second, they immediately throw it on the table or ground, shocked and scared sometimes!
Then they pick it up later to inspect it. One of my top 3 favorite tricks, easily, as it is so simple to perform, yet so hard hitting.
Its easy to come up with a signed card version, too, but I wont reveal my handling of that here.
PM me if you really are curious though.
Good luck.
All the best,
-Sanj