Marble Run by Quadrilla

In our opinion, building toys get you the most bang for your toy-buying buck. Blocks, train tracks, logs... you get these toys when your kids are young and -- if our own childhood is anything to go by -- they'll be played with for years. These build-your-own marble runs fall into the same camp. Not only do you get the fun of designing an endless variety of runs, but you also get a lesson in chaos theory as you watch the marbles move along the tracks. It's where art meets engineering and physics.

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The quality of Quadrilla's German-engineered wooden blocks and twists makes this a keepsake toy that will last for years. And like any good building toy, you can start with a decent basic set, such as the one pictured at the left, and keep adding as many expansion kits as you want... until you can ostensibly create a complex masterpiece such as the one at the top of this post.

Basic set ($59.95) at Playfair Toys. There's also a smaller "Try Me" starter set ($44.95).