Other
Birmingham Southern College: Organ History
This site provides very useful information on the history of the organ, what the organ is, and how it works. The geographical tour features organs in England, Germany, Italy, and France and offers information and pictures.
Other
Historic Organs: The Organ in America: A Historical Sketch
This is the history behind the organ in America.
Other
American Theatre Organ Society
This site has a lot of information, including articles about theatre organs, their history, how they work, where they can be found, and artists.