Blind Watchmaker Applet
The Blind Watchmaker Applet demonstrates how random variation and non-random selection can combine to form interesting and complex shapes. The gist is that you step through a process where 12 forms are created by small and random variations on a set of genes. At each step, you choose a form to be the parent for the next generation.
I was a little disappointed to discover that I could still get semi-interesting forms by consistently choosing the same slot over and over, thus removing the selection component. On the other hand, the forms I got by actively selecting were more interesting and complex, so it does still demonstrate the power of selection. And it is just a simulation after all.