NOTE: Clocktower Books, Far Sector SFFH, and related projects are so rich in historical and thematic cross-references on the Internet that here is now a special References page for your convenience.
Encyclopedia of Science Fiction (ESF)
Encyclopedia of Science Fiction (ESF) online and current.
Far Sector SFFH at Encyclopedia of Science Fiction (ESF) (ed. Mike Ashley).
Magazine titles: Outside 1998, Deep Outside SFFH 1998-2002 eds. John T. Cullen and Brian Callahan; Far Sector SFFH 2002-2007 ed. John T. Cullen.
ESF Wikipedia page including info on latest print & online editions, etc.