Sometimes the challenge of just completing a puzzle isn't enough. When you're trying to prove you're better than your friends you need a specific metric to validate your superiority. So this puzzle, made of randomly-shaped pieces that assemble into a perfect cube, has a built-in timer that starts when the cube breaks apart, and stops when you've successfully re-assembled it.
The $US20 Crash Cube also remembers the fastest time the puzzle was solved in, so you can compete against yourself to best your own record if you don't actually have any friends, or if they long ago got tired of your over-competitive spirit. [Toysmith]