My favorite teaching tool!  Make your own movable Circle of Fifths.  Download as a PDF right away.
 
Watch a short video to see how it goes together 
 
The original Pythagoras Circle of Fifths (over 2,000 years ago) shows frequencies so the circle runs the opposite way.  Many circle of 5ths still are orientated the original way but music moves from V - I and this circle shows the way music moves as a clockwise movement.  It is still a circle of 5ths because C is the 5th of F which is the 5th of Bflat, etc. etc.