A unique collaboration of over 150 acclaimed art museums in 40 countries. The search capabilities are very clunky and it is recommended to use the Search by Museum category to browse. Add images to "Your Gallery" (allows you to save selected works you like or would like to easily find again.)
Developed by the University of Michigan School of Art and Design, Mother of All is an extensive set of links to research resources, image collections, online digital art, art schools, art departments, and art museums.
Artcyclopedia
A guide to museum-quality fine art on the internet, primarily painting and sculpture. Great for finding images of the actual artwork!
ArtSource
"...a gathering point for networked resources on Art and Architecture. The content is diverse and includes pointers to resources around the net as well as original materials submitted by librarians, artists, and art historians, etc..."