I kept a listing of virtual globes in 2005 and 2006, but it's now woefully out of date http://geography2.blogspot.com/2005/11/listing-of-virtual-globes.html. Today, the main four seem to be: Google Earth (proprietary and free), Microsoft Bing Maps 3D (proprietary and free), ESRI ArcGIS Explorer (proprietary and free), and NASA World Wind (free and open source). Many, if not most, are being integrated into the web browser.
What is out there? Any special or particularly innovative capabilities?