The Google Maps API lets developers embed Google Maps in their own web pages with JavaScript. You can add overlays to the map (including markers and polylines) and display shadowed "info windows" just like Google Maps. : http://www.google.com/apis/maps/ Various hack projects ; http://www.gcensus.com/index.php (combines Google maps and U.S. census data), http://www.housingmaps.com (combines real estate listings with city maps from Google Maps), http://supergreg.hopto.org/google-yahoo/ (meshes traffic data with googlemaps), http://www.ahding.com/cheapgas/ (combines with gassbuddy.com's gas price database).

A9.com Maps did some amazing work integrating their local search photos into their maps. (still available?)

The Earth Imagery Source ; ResMap provides free online access to GIS-ready satellite data. : http://www.resmap.com/

Art Source International : selection of Replogle Globes, Rare and Antique Maps, Historical Maps, Antique
Atlases, Antique Prints, turn-of-the-century reproduction posters, historic photographs http://www.rare-maps.com/