Odden's bookmarks
World reference website for maps and geography: thousands of commented links, accessible through directories and through a search engine.
http://oddens.geog.uu.nl

Geomapping
Portal of cartography: thousand of links towards maps of all kinds.
http://www.geomapping.com

World of Maps
Directory of thousands of maps, organized in country and subject directories.
http://www.maps.ethz.ch

Perry-Castañeda Library Map Collection
Extensive collection of maps for countries and cities in the whole world.
http://www.lib.utexas.edu/Libs/PCL/Map_collection