SilverlightEarth.com is a Microsoft Silverlight-based map viewer, supporting Microsoft Virtual Earth, Google Maps and Yahoo Maps image tiles (satellite, road and 'hybrid' views).
Supports
Gaml - Geographic Application Markup Language.
Microsoft Silverlight 1.0 is required: INSTALL NOW.
There is also a
Silverlight 2.0 (Deep Zoom) Virtual Earth/Google Maps/Open Street View version.