ArtLex
Art Lex: Rhythm
This site from Artlex provides a thorough definition of the Principle of Design known as Rhythm. There are links to other sources and terms as well as visuals from artists such as Klee, Matisse and Mondrian that show further examples.
NPR: National Public Radio
Npr: King Gimp Revisited
Site from NPR includes an interview, video clips and links about expressionist artist, Dan Keplinger. This artist has overcome his disability to create fine art that expresses himself.