Until there's a virtual blues club, there's Pandora.com. Reading about the blues is one thing, but actually getting to listen to the music and the people who made it is another thing entirely (so do both). Explore new music by letting Pandora recommend artists related to the ones you already know. One suggestion: Start a channel for each style of blues based on one of its representative figures (ie, Bessie Smith for the classic blues; Charley Patton for the folk blues, etc.).
The Smithsonian Folkways Collection offers 24 one-hour programs showcasing different parts of the incomparable Folkways archive. Start with the Blues episode (program nine), and then explore from there.
The PBS website currently hosts some great resources related to the Smithsonian Institute project The Mississippi: River of Song. Of particular interest is the article "At Play in the Delta" by Michael Luster, a study of music, recreation, and the history of the Delta region.
Another Smithsonian essay hosted on the PBS website. Bill Monroe, one of the leading authorities on rural American music, has put together an article on the development of Southern music and its emergence as a substantial force in American culture in the first half of the twentieth century. Excellent reading for fitting the history of the blues within a larger context of Southern cultural production.
The Blue Highway website has links to all kinds of information on the blues. The mini-biographies of 20 key blues musicians offer a nice primer to who is who in the blues, and the portal to the additional essays page links up a lot of writing on many aspects of the blues.
The Library of Congress offers a truly incomparable resource in its digitized version of the John Lomax southern recording trip 1939 archive. The legendary ethnographer John A. Lomax logged more than 6,000 miles recording and documenting folk culture across the American South for the Library of Congress in the late spring of 1939. This is the historical treasure trove he produced.