Princess Card Trick by Royal Magic
A spectator is shown five cards and asked to merely think of one. They have a completely free choice, which is never revealed to the performer.
The magician studies the cards and removes one, placing it in his pocket. When the cards are again show to the spectator, one is missing - their mental selection!
The trick is easy to do, requiring no sleight of hand to perform. Specially printed cards do nearly all of the required work.