If you are a fan of Rube Goldberg-style contraptions, you will love Think Geek's Cological Marble Run Construction Set. It contains everything you need to create your own marble mayhem—including 23 different types of marble-moving mechanisms like rolling cars and whacking mallets. More info and a video after the jump.
The instruction manual teaches you how to use the parts, but leaves the course design up to you. The whole thing is in Japanese anyway, so don't expect to do a whole lot of reading unless you can speak the language. Real geeks don't need any stinking instructions anyway. Available for $69.99.[Think Geek]