Microsoft has just released Virtual Earth 3D which complements our local.live.com map offering by running directly in the browser window. If you are familiar with Google Earth, this is a similar concept but with more integration with browser search and of course without the desktop application.
After I installed the plugin for IE7, I checked out a few locations like London and San Francisco (below). I see this becoming a really useful tool once more and more buildings get mapped in 3D. At the moment most of the big cities have portions of buildings mapped in 3D - by the looks of it they are creating a 3D model and then applying a skin from photos of the building, as can be witnessed on the Tower of London.
Update: Currently the following cities are covered San Francisco, San Jose, California, Seattle, Boston, Philadelphia, Los Angeles, Las Vegas, Detroit, Phoenix, Houston, Baltimore, Atlanta, Denver, Dallas, and Fort Worth, Texas. So make sure you check them out first. More are being added soon.
What I really liked was Mount Everest (below) which showed me the type of view you could experience should you be brave enough to climb to the summit.
Make sure you experience this for yourself! (search for a city then click 3D)
Learn more about 3D maps
The only question I have remaining is that when you line up Virtual Earth 3D against Google Earth, which is the more "Web 2.0"?