1) P.H.S.N.E. (Photographic Historical Society of New England).
2)The Daguerreian Society / Pittsburgh, PA
3) Metropolitan Post Card Club of New York City. A terrific historical resource of the artists, photographer's, publisher's, etc. of post cards.
4) Cycleback.com. A guide to judging the authenticity of photographs.
5) Luminous Lint. For collector's and connoisseur's of fine photography.
6) Stereoviews.com. THE website for stereoviews, and much more.
7) Photo Central.
8) Dennis A. Waters Fine Daguerreotypes.
9) Jeffrey Kraus Antique Photographica.
10) Christopher Wahren Fine Photographs.
11) KaufmaNelson Vintage Photographs.
12) Stereographica.com. Antique Photographica.
13) Greg French Early Photography.
14) Paul Frecker London-Nineteenth Century Photography. An online gallery selling various formats of antique photography.
15) The Library of Nineteenth Century Photography.
16) Jan Lagendijk's Stereoview Heaven. Fine stereoviews from 1860 to the early 1900's.
17) Pierre Spake Photography. Photography, Works on Paper, Works of Art.
18) MyDags.com. Dan Hadley Proprietor.
19) Vernacular Photography- Great images by as-yet unappreciated and undervalued artists.
20) Andreas Wiemer-American Presidential Autographs.
21) Lanterna Magica / Libreria-Galleria-Edizioni.
22) Playle's Online Auctions. As well as a link to multiple dealers of post cards, ephemera, etc., this site contains an excellent reference guide to the dating of real photo post cards.
23) Biblio.com An excellent online source for collectible books, many of them photography.