If you're an engineer, physics geek, or just liked to play with legos and tinker toys as a kid, you'll probably like this.
http://fantasticcontraption.com/
What You Start With: http://fantasticcontraption.com/?designId=106294
A Clever Idea to Finish With: http://fantasticcontraption.com/?designId=106362
Bad Example: http://fantasticcontraption.com/?designId=105753
Good Example 1: http://fantasticcontraption.com/?designId=108498
Good Example 2: http://fantasticcontraption.com/?designId=110321
And finally check out this ingenious idea: http://fantasticcontraption.com/?designId=15560
A buddy sent me all the ones he's figured out. I"ll post them later as the simplicity of his designs makes you wanna kill him.
Goodluck!