This idea came from here. Martina made these using cardboard she cut into squares instead of the wood squares. Then she mod podged the patterned paper on each side. Be sure to let these dry VERY well (at least 24 hours) before stacking them and don't put a lot of mod podge, if any, over the top of the paper to prevent sticking.
I found a bag of wood squares (in a variety of sizes) at Michael's for 2.99. The bag had small, medium, and large squares in it. The large squares would be the perfect size for a memory game and there were plenty of the large size to do it.