About time I had my own Dry Erase slate a.k.a Clapper a.k.a ClapBoard. I ordered this 9 x 11 dry erase slate from Amazon mainly because I had a gift card and shipping was free at the time. This one feels like it has some magnets on the top so as the clapper gets closer it actually snaps in place. Feels like a wooden top and the slate area is a thick acrylic. I personally think it also looks better than the other cheaper ones. If looks is of no concern, cheaper ones like the Pearstone go for about half the price of this Ikan over at B&H.
Cheapest of all the ones i've found is the very generic White 9 x 11 Director's Clapboard via Amazon (below).