This is one of the oldest effects I know. While cleaning out some old magic bins I came across cards for this trick (several different packets of them) and thought it would be fun if this effect could be done online. You can do the trick below, if you would like to make this trick you can find the explanation here.
Think of a number from 1 to 63. Then check the boxes below that have the number your thinking of in it. Leave any boxes missing your numbers unchecked. Then press read my mind to see if I can figure out your number.