My FAVORITE card trick!
Allow your spectator to choose a card. Tell them you have the ability to read minds, you just need to extend your range. You extend an antenna out of your pocket. After the roaring laughter subsides you tell your spectator to focus on their card an you will know exactly what it is. While they focus you take your antenna out, which happens to be a telescoping dental mirror. This gets a laugh as everyone but the person with a card is in on the joke. You apologize for cheating and reveal that their card has been on your mirror the whole time.
A wonderful trick and bit of comedy in one!