I came here to recommend magna-tiles. My son is 9 now, and he still plays with them on a regular basis, and his friends do as well when they come over. He knows

I came here to recommend magna-tiles. My son is 9 now, and he still plays with them on a regular basis, and his friends do as well when they come over. He knows what a cube looks like spread out in two dimensions, and a number of other shapes as well. They're just plain fun to play with they, make a really satisfying sound as they snap together, and it's not a big deal when your creation collapses every once in a while. A simple microscope is amazing to a young kid as well.