Rotating Chains by Akiyoshi Kitaoka
The blue and yellow circles made up of what look like bicycle chains appear to spontaneously rotate. Try focusing your attention on only one of the six circles at a time and you should find that the one you are focusing on stops moving. If you want to maximize the motion effect, move your eyes around this image rapidly. As your focus moves from circle to circle, the perceived motion increases significantly.
(via Akiyoshi Kitaoka)