One of the places I frequently visit on the internet is the506. While the506 is best known for its weekly color-coded NFL broadcast maps, this site also has a great set of well-run forums with many quite knowledgeable members. (Note: free registration required to access the forums)
The forums cover sports broadcasting topics such as weekly TV/radio schedules and announcer listings, analysis of media rights packages, reviews of broadcasters, discussion of TV ratings, network scheduling, announcer assignments, etc.
My favorite section (and the one most relevant to this blog) is the Sports Broadcasting History forum. I am one of a set of members who has been researching various aspects of sports TV history. For example, we have created year-by-year historical TV schedules with game times, networks, and announcers and have collaborated to identify errors and fill in missing pieces. I've done a lot of work on the historical college basketball and college football listings, while other members have compiled similar listings for other sports such as the NFL (including AFL and AAFC) and MLB.
If you are interested in sports media (past or present), I highly recommend checking out the506.