Rathkamp Matchcover Society — RMS is the premier organization for collectors worldwide; https://www.matchcover.org
The Matchcover Vault – excellent reference site for the hobby; https://www.matchpro.org
Website of Flemming Hennigsen — website of well-known collector from Denmark displaying much of his extensive collection; http://phillumeny.dk
Oh, What a Match — website of two collectors in the United States presenting an interesting view of collectors and the hobby in general; ohwhatamatch.com