Tomb of the Unknown Soldier - Washington, D.C.
When I saw this site originally, I thought it was the White House. It was only after I "bing mapped" it that I realized it was actually the Tomb of the Unknown Soldier. This photograph was taken on the same plane ride as the photo of the Pentagon.
Bing maps' bird's eye view is quite a cool little tool and at least the imagery might offer some good competition to Google maps. The search tool needs some work though. When I typed in the White House, it search for businesses with that name whereas Google knew what I was asking for right away.