Road Map Collectors of America  
   RMCA is a group of road map collectors throughout North America and Great Britain.
   http://www.roadmaps.org/

David Rumsey's Map Collection  
   Thousands of high-resolution digital images of maps from the David Rumsey Collection, one of the largest private collections of historic maps in the US. Focus is 18th and 19th c. North and South America cartographic materials.
   http://www.davidrumsey.com/

International Antiquarian Mapsellers Association (IAMA)  
   The IAMA's main purpose is to promote the professional trade of antiquarian, collectible maps and related books combined with promoting public interest, appreciation and education with respect to antiquarian maps.
   http://www.antiquemapdealers.com/

International Map Collectors Society  
   London-based organization for those interested in maps, including collectors, dealers, librarians, and academics. Activities overview, events calendar, journal, library, and resources.
   http://www.imcos.org/