All the World's Rotorcraft: Provides pictures and background from the first designs to current machines. Also offers dictionary and links to related resources.
Blueghost Green: History of this helicopter cavalry troop from the Vietnam War era of helicopters.
Helicopter History Site: This site traces the evolution of rotary wing aircraft back to Leonardo Da Vinci.
Helicopters and Autogiros 1939 to 1945: Aviation history in the WWW: Index of aircraft by category and time period.
Igor I. Sikorsky Historical Archives, Inc.: Dedicated to acquiring, preserving and protecting the historical materials that chronicle the aviation careers of Igor Sikorsky, the companies he founded and the accomplishments of its employees.