Chess Dryad
Devoted to the history of California Chess, 12,667 chess games suitable for downloading into ChessBase, a large collection of articles and photographs, Shorman's thirty rules, and much more.

Chess History Center
Service center for serious chess historians, clearinghouse of research requests and index to web resources.

Chess Variants Pages
Comprehensive site with rules, information, histories, and links for a large number of chess variants.