Michel Houde: Security Markings on British Malaya, British Consular Post Office at Bangkok, Thomas Waghorn.
Ralph E. Trimble: A site devoted to the study of re-entries on postage and revenue stamps of BNA, U.S.A. & the world.
retroReveal - “…web-based image processing algorithms designed to help people discover hidden content.”
Stamp Compare – “…is to make it easy to perfectly align two images and then "toggle" between them, to manually compare and identify any differences.”
PHILATELIC EXPERTS - “… the names and areas of specialisation of some 2000 individual stamp experts, mainly pre-2000, who have back stamped or hand signed postage stamps, or issued certificates.”
Stamp forgeries of the world – “…vision is to display all forgeries ever created next to a genuine stamp for easy comparison.”
APEX Certificate Archive - "... search and view the opinions of stamps and covers that the American Philatelic Expertizing Service has examined."
Stamp Printers - "A worldwide stamp production resource from 1840."
David Rumsey Historical Map Collection – “… focuses on 16th through 21st century maps of North and South America, as well as maps of the World, Asia, Africa, Europe, and Oceania.” And more.
Time and Calendars - Calendars, Chronologies, Eras, Calendar units, etc.
Perpetual Calendar - A helpful tool for the Postal Historian
Preservation and Care of Philatelic Material
W.C. Burden: Small Queen CPV Project