Some Optical Illusions by Akiyoshi

Akiyoshi Kitaoka is a Professor of Psychology at Ritsumeikan University in Kyoto, Japan, and he has made some killer optical illusions.

 Rotating Snakes

The classic, that most people are familiar with. The use of snakes are cool in this one as there's some allusion here to the ancient symbols of the ouroboros and mobius strip.

 Autumn Color Swamp

This one's a seasonal choice - scroll up and down.

Rice Wave

 And finally, a piece that was used for the album cover of Animal Collective's Merriweather Post Pavillion (2009). A great album and a great cover. Have a listen if you haven't before, also an awesome video. Also, here is Akiyoshi's website for more.