This is an extraordinarily impressive site. The home page is primarily and index, with links to a vast number of sub-sites. The Photo Gallery offers a slide show, there is a Timeline of San Diego history, Biographies of notable San Diegans, and many other attractions. The thing I find most interesting is the collection of postcards from the Expositions which have been held in Balboa Park. Just as an example of the treasures of this site, take a look at these hand-colored postcards from the California Pacific Exposition of 1935-36.
There is also an on line sample of an exhibit of local landscape artists currently running (through March 2nd, 2002,) at the San Diego Historical Society Museum.
I have spent many hours perusing this site, and still haven't seen it all. It is well worth a visit.