Caution: This page contains some works of "anomalous motion illusion", which might make sensitive observers dizzy or sick. Should you feel dizzy, you had better leave this page immediately.
Some of the pictures on this website can cause dizziness or might possibly epileptic seizures. The latter happens when the brain can't handle the conflicting information from your two eyes. If you start feeling unwell when using this website, immediately cover one eye with your hand and then leave the page. Do not close your eyes because that can make the attack worse.
J-Walk points to a blog about Optical Illusions. It has links to some great illusion sites:
53 Optical Illusions | Perceptual Science Group | Motion Perception | Project Lite | The Museum of Unworkable Devices | Planet Perplex