Illusion
Optical Illusions - From EncycloZine (Y, M, O, T)
Exploratorium - An online science museum of optical illusions (Y, M, O, T)
IllusionWorks - "the most comprehensive collection of optical and sensory illusions on the world-wide web" (Y, M, O, T)
SandlotScience - Online science museum with both online and downloadable illusions (Y, M, O, T)