For many years Microsoft provided a WMS that included USGS topos and US aerial photography. Popularly known as TerraServer (or Microsoft Research Maps -MSRMaps), the service no longer exists as of 5/1/2012, meaning that the Google Maps mash-up I created using the data no longer work. For more info on TerraServer’s death check out the post on Directions Magazine’s All Points blog.
No worries from my end, as the use of that pages was nearly non-existent! People are way more interested in my OpenLayers Google Mash-Up . I’ll update my links accordingly, again, not that it matters because people weren’t interested in Microsoft’s WMS service. Thankfully today there are many, many more options for streaming high quality basemap data through web mapping applications.