I Found the Strangest Things on My Way Here

A nice collection of visual black/white/gray optical illusions are available at Light Demonstrations. First the illusion is animated (very quick load even with dial up) and then the science is explained. I know, this site might even have some practical application. But it's neat to have your eyes play tricks on your mind. Even when you know what to expect your brain still gets the wrong signals. You can even run this site with a monochrome monitor.