Intriguing Color Illusions
I found this very cool site of illusions via this thread in AskMeFi, tons of them. I'd like to try a painting using this type of color juxtaposition to create the illusion of intensity.
This website is from the psychology department of a Japanese University in Kyoto.
I also liked the Vanishing Circle Illusion and Roulette.
These can take a few seconds to load.