I use this: http://www.amazon.com/gp/product/B004AKQ3UW/ref=oh_details_o01_s00_i02?ie=UTF8&psc=1
It gets the job done. On the plus side, I can cut the magnet to size. Also the back side is adhesive.
On the negative side, they will hold the sprite up, along with a few sheets of paper, but not much else. There are many stronger magnets out there. Also, I've had a couple of them have the adhesive fail over time, but that's nothing some e6000 won't fix.