Mapping and Geospatial Imagery 

A highly selective list

Google Earth is a virtual globe providing satellite imagery, maps, terrain (often in 3D view), 3D buildings. Layers showing additional imagery and data can be turned on or off. Add photographs or additional data to create customized maps. View shared maps in a community on the World Wide Web.  Available for free download; 5.0 is latest version.  New imagery and layers have been added, including ocean floor terrain, and most recently, the terrain of the Great Lakes. A professional version for commercial use is available for purchase. Tutorials show how to use the viewer and describe new features.  Originally created by Keyhole, Inc., which was acquired by Google.  The markup code,'Keyhole markup language', or .kml extension, can be written using GeoServer.  A Wikipedia article describes Google Earth in detail.

KML FactBook utilizes the Google Earth viewer to visualize CIA Factbook data.  Help page gives instructions for creating and uploading new kml files from Google Maps or Google Earth.

Virtual Earth from Microsoft provides a free Web based viewer called Live Maps.  It is similar to Google Earth, but differs in a few crucial ways.  It is a web based viewer, while Google Earth is a separate viewing platform.  It provides imagery at high resolution, sometimes from different sources, and in some places at higher resolution, than available in Google Earth.  Buildings can be viewed at low angle and rotated.  3D views are available.  The free viewer does not permit creation and sharing of maps using its platform.  Data added in files to share is possible only to organizations that purchase enhanced versions.  A Wikipedia article describes Live Maps in detail.