MagFormers, for the visual types. Beyond expensive, but for us, super-cheap on a cost-per-hour used basis (Grandma built up the collection over a couple years of birthdays and Christmas). Basically, you lay out your figure in 2D magnets, pick it up from the right spot, and voila, a 3D shape. Mr. Spatial loved to torment me - "Mommy, guess what shape this will be!!!". Linear me: "uh.... a rocket?". Him: "Oh Mommy, how can you not see this will be a dodecahedron?"
Looks like all the other magnet building toys out there, but really gets used differently. And still weekly (DS10 and DD7).
