Illusions and Explainations http://www.michaelbach.de/ot/
kids illusions http://kids.niehs.nih.gov/illusion/illusions.htm
wikipedia http://en.wikipedia.org/wiki/Optical_illusion
How Optical Illusions Work http://www.visualillusion.net/
3D Illusions http://www.vision3d.com/whycant.html