• Cornell University Library, Making of America digital collection

http://ebooks.library.cornell.edu/m/moa/

• Deltiology 101

http://www.jewelspostcards.com/del.htm

• Library of Congress, Map Collection

http://memory.loc.gov/ammem/collections/civil_war_maps/

http://hdl.loc.gov/loc.gmd/g3700m.gct00185 (1839 map of Pennsylvania and “West” Virginia)

• Metropolitan Postcard Club of New York City

http://www.metropostcard.com/

• New York Public Library: digital collection

http://digitalgallery.nypl.org/nypldigital/index.cfm

• Perseus Digital Library,  Tufts University

http://www.perseus.tufts.edu/hopper/

• The Postcard Album, by Helmfried Luers

http://www.tpa-project.info/

• The Thomas Minor Society, the descendants of Clement Minor, ancestral number 1312.