I got a leaked copy of the Spore Creature Creator demo and have been playing around with that. After succumbing to my inner 8 year old and making a penis monster, I started to make some...interesting things. It's surprisingly easy to make shit without needing to read through a giant manual.
I wasn't going to download it, but after watching that video of Robin Williams making a monster of his own, I had to try it:
http://www.youtube.com/watch?v=V5TXEUiR1Xk