This is the virtual home of the David Rumsey Map Center, located in Green Library, Stanford University. The entire David Rumsey Map Collection, with over 50,000 of the items online at davidrumsey.com will be coming to Stanford University Libraries and reside at the David Rumsey Map Center (DRMC)....

A hover/click opaqueness background effect that makes images visible when specific points are hovered, showing some content once clicked.

Leaflet is a modern, lightweight open-source JavaScript library for mobile-friendly interactive maps.

Stamen Design is a pioneer in the emerging field of creative mapping and online data visualization. We design and build thoughtful, engaging and impactful interactive projects for many of the world's most public organizations and brands.

Worth a quick mention: The University of Chicago Press has made available online -- at no cost -- the first three volumes of The History of Cartography. Or what Edward Rothstein, of The New York Times, called 'the most ambitious overview of map making ever undertaken.' He continues:

An interactive journey where a Canvas map path is animated according to the content that is scrolled on the page.

Unfolding is a library to create interactive maps and geovisualizations in Processing and Java. Mapping Library For Processing And Java

Georeferencing: maps already referenced

The Lionel Pincus & Princess Firyal Map Division is very proud to announce the release of more than 20,000 cartographic works as high resolution downloads. We believe these maps have no known US copyright restrictions.*