Cuboro

This gift idea makes me sad that it's so expensive, because it's also really cool. Cuboro is a set of wooden blocks with grooves and tunnels for marbles to roll through. By stacking the blocks atop or next to each other, you can create complex, twisty pathways for marbles to roll through. It sounds like a lot of fun, but the starter set has 30 blocks for $119 USD, or about $4 per individual block!