Specialty Publishers
These are mostly small specialty publishers. If you are looking for something a bit different or out-of-print, these are good places to check out.
Arkham House The classic publisher of fantasy and horror. They also carry books from Fedogan and Bremer.
Donald Grant A long time publisher of fine limited editions specializing in fantasy.
Hobgoblin Press A small press dedicated to the best old horror stories and novels and to developing new authors.
Meisha Merlin Press Dedicated to printing the best in science fiction, fantasy, and horror. They have both old and new stuff and are always worth checking into.
Necronomicon Press Works of H.P. Lovecraft and other old and new writers in the horror field.
NESFA Press The New England Science Fiction Association press. They are reprinting a lot of early science fiction that is otherwise unavailable.
Wildside Press - Lots of interesting off-beat stuff and reprints o long out of print items. Well worth a visit.