The invention of the radio harkened a new age. The technology uses radio waves which power radio instruments, and was originally called "wireless telegraphy." Originally developed in the 1880s, the first successful transatlantic radio broadcast was achieved by Guglielmo Marconi, who is commonly thought to be the inventor of the technology. Clearly, that's not exactly true, although the term "radio" came into use after his transmission across the Atlantic.
Regular Websites
About.com: The Invention of Radio
Delves into the invention of the radio and all of the technological developments which made that invention possible. - About.com: The Invention of Radio
http://inventors.about.com/od/rstartinventions/a/radio.htm
History of Radio, First Thirty Years
The focus of this website is on the years between 1895 to 1925, rather earlier than the usual timeline, which starts around 1940. Also has numerous images from the era. - History of Radio, First Thirty Years
http://ns1763.ca/radio30/radio-first-30yrs.html
Beginning with Marconi in 1895, this site chronicles the beginnings of radio, including Fleming's valve and crystal detectors. - History of the Radio Receiver
http://www.radio-electronics.com/info/radio_history/radiohist/hstrx.php
Radio Days: Broadcast Journalism and Historical Events
Profiles commentators, including Edward R. Murrow, Eric Sevareid, Sigrid Schultz, and Drew Pearson, as well as radio events such as the Hindenburg disaster, Pearl Harbor, the Battle of Iwo Jima, and the funeral of Robert Kennedy. - Radio Days: Broadcast Journalism and Historical Events
http://www.otr.com/news.shtml
The Work of Jadadis Chandra Bose
Chronicles the work of Jagadis Bose the polymath who pioneered, among other things, solid state radio, archaeology, plant science, and microwave optics. - The Work of Jadadis Chandra Bose
http://www.tuc.nrao.edu/~demerson/bose/bose.html
United States Early Radio History
Rounds up information about the history of the early days of the wireless, or radio as it became known. It has an overview, an account of the history of the electric telegraph, telephone, and finally, the wireless radio. - United States Early Radio History
http://earlyradiohistory.us/