This is a great self working card trick
Performance: Take 21 cards and deal them out into three columns by dealing seven cards in each column. Deal three cards across for the first row, then another card on top of each for the next row, and so on until you have seven rows of cards in three columns for a total of 21 cards. Make sure you deal out each of the rows so you can still see the cards behind it.( See picture below)
Now have someone think of any card in one of the columns, and then tell you which column the card is in. Pick up one of the other columns, then the column he chose, and then the last column, so that the column with the chosen card is between the other two.
Deal them out again the same as before, and have your volunteer tell you which column the card is now in. Again, pick up the cards so that the column he pointed to is between the other two.
Repeat the process of dealing out the cards, having him tell you which column his card is now in, and picking up the cards so that the column with his card is between the other two columns. You have now done this three times, and it's time to find his card!
Hold the cards face down in your hand, as if you were going to deal them out again, but instead ask your volunteer if he has ever heard of the magic word ABRACADABRA. Say that not many people know it, but ABRACADABRA is a magic word for finding things, and that you'll show him what you mean.
Spell the word ABRACADABRA, and for each letter deal one of the cards face down on the table. When you reach the last "A", pause, and then turn over that card. It will be the chosen card! As long as you spell ABRACADABRA right, this trick will work everytime!
source : www.goodtricks.net