"The best packet trick of the 20th century." - Eugene Burger

Prediction of a thought of queen, with a three phase revelation.

You bring out four cards and ask your spectator to name any queen. You then cleanly spread those four cards on the table. The only face up card is the chosen queen. Then you turn it over and it's back is a different color than from the rest of the cards. As further proof that you already knew queen they would say, you turn over the rest of the cards and they are all completely blank.

Powerful effect with little setup.
Three phase construction builds to a dramatic conclusion
Takes up little space (1mm) in wallet, and can be with you at all times.
Requires no sleight of hand
Can be performed as a mental demonstration (prediction) or as a magical effect