- General Websites
Mackay, James A. The World of classic stamps.
Catalogs - Print
- Michel's Klassik-Katalog Europa 1840–1900
- According to Michel's website: "ca. 700 Seiten, über 2800 farbige Abbildungen, rund 75 000 Preisnotierungen." Published October 2007. I do not know if there has been more than one edition.
- Scott. Classic Specialized Catalogue of Stamps & Covers.
- Annual since 1995. Book & DVD versions; note that the later pdf versions had the print function disabled. Available for the iPhone and iPad as of 2012 (discontinued in 2014).
- Yvert & Tellier. Classiques du Monde: 1840-1940.
- Published every 5 years. Latest edition is 2010.
Worldwide Stamp Catalogues is a website that lists catalogs, print and online, for all countries.
Here are the online catalogs that Keijo Kortelainen has reviewed on his Stamp Collecting Blog:
Individual Countries (Web)
Stamp Domain Resource Pages.
A good place to start for online and print resources for a variety of countries.
Comparative Stamp Forgery Identification Site
Stamp Forgery Guide.
Sources for Information on Forged Stamps and on Stamp Expertising.
Stamp Forgeries of the World.
Goal is to cover all countries with ten thousand images of forged and genuine stamps.
StampSelector Scarce Stamp Quantities Issued List.
"This listing is a perpetual work in progress - an incomplete listing of stamps with printings of 100,000 or fewer. It currently contains over 9,700 entries, and will be updated periodically."
Internet Resources for Postal History Research.
"An annotated listing [by Richard Frajola] of online resources that have been found useful in general postal history research.