Classic TV Archive
Not the fanciest looking website, but you'll find lots of well-researched episode guides here for both obscure and popular TV shows of the golden age of television.
This site probably has more episode guides than any other site on the web. There are plenty of bells and whistles, including Flash animation (which may make page loading very slow if you don't have a brand new computer). The one caveat is that the information isn't 100% reliable, and there's rarely any indication of where it came from - although a careful review will tell you that much of it has been "borrowed" verbatim out of books or other websites.
Episode lists for over 3600 shows. Most contain links to for further information.

One of the best sites for TV news and schedules.

TV Shows on DVD
If you're looking for news about upcoming TV DVD releases, or want to know which shows have already been released, this is the place to go.

Museum of Broadcast Communications
Headquartered in Chicago, this non-profit organization used to offer streaming video of classic TV shows - everything from Dragnet to political events, to more modern shows like CSI and ER. But the response was overwhelming and they didn't have the resources to keep up, so they disabled this feature. There are still a few videos in their featured online exhibitions, and one can only hope that they'll be able to offer a more extensive catalog again in the future.

Shokus Internet Radio
Stu Shostak, who's been selling classic TV shows for decades through his Shokus Video company, is the man behind this internet radio station for baby boomers. The station features old time radio shows that went on to become TV shows, lots of music (big band, adult contemporary, rock - even hip hop), and interviews with TV celebrities and historians. Highly recommended.

News From ME
"A weblog about TV, movies, comics, theater, news, politics, and other forms of fantasy." Television/comic book writer Mark Evanier is an expert on various topics, including television and animation, but the most important reason to read his blog is that he's funny, provocative, and entertaining. Also highly recommended.

Perry Mason TV Series
Loads of information about one of the great TV shows of the 1950s, courtesy of PM fan Big Dave Brockman.

Classic Themes
This site has information not only about TV and radio themes, but also about the shows themselves.

Variety Obituaries
Keep up with all the latest Hollywood deaths.
A directory of arts-related websites.

Invention of Radio
Outline of radio's early history.

Television, Radio and More - The History of Great Inventions!
Resources on the history of TV and radio.

Hollywood Memorabilia
Entertainment memorabilia and collectibles.