Exploratorium
Exploratorium: Online Exhibit: Mix and Match
A Shockwave movie which allows users to mix varying colors of light and observe the effect upon the appearance of a circle. Accompanied by a "To Do and Notice" section and a "What's Going On?" section. Excellent!
Other
Museum of Web Art
A fascinating site devoted to art and graphics used on the world wide web. Explore the best in buttons, banners, counters, and more.