Atwater Kent Radio: A collection of radios and information by Vane Warner 
Bang & Olafson Product History DK 
Bellingham Antique Radio Museum
Bliley Electric Company 
Broadcast Pioneers Library: University of Maryland. Includes soundbites.
Vintage Radio and Communications Museum of Connecticut
The Charles Herrold Story 
The Creative World of Stan Kenton
Jeff Miller's Collection A collection of articles on radio history.  Good reading.
Nipperscape: History on the RCA dog
Radio Days
The Nicola Tesla Home Page
On The Short Waves
United States Early Radio History By Thomas H. White. Lots of intersting reading.
Vintage Radio and Communications Museum of Connecticut 
100 Years of Radio: From Italy