Why is watching a marble snake its way around a twisty maze so mesmerizing? Maybe it's an allegory on the human condition as we all try to make our way through the world? What's for certain is that they make for great desk toys, and as long as your office gets a bit of sun during the day, this one could—at least in theory—keep running until our local star eventually burns out.
The $35 kit is all-assembly-required too, letting you finally put all of your Ikea skills to good use as you wire up the electric motor and solar cell, sync the gears, and basically procrastinate on that Excel sheet you should have really finished hours ago. Just don't go gifting it to some kid and claiming it's a legit science project because they'll be heartbroken when they eventually learn they didn't solve perpetual motion. [ThinkGeek]