Add-Art is a Firefox addon that replaces website advertising with art. Originally developed in 2008, the 2.0 release allows users to choose between different sources of art from The Brooklyn Museum, Eyebeam, Kadist Foundation, NASA, and Rhizome.
The plugin works alongside AdBlock Plus, which blocks online ads, and replaces that blank space with art images.
More infotmation at Add-art.org and code at GitHub
Thanks to Corey Tegeler