Google Earth

Googel Earth is currently in Beta (with a limited number of downloads). It's a great tool, and I expect many people to use it in the future.

However, it leaves a very large cache file on the HD, and it would be nice if a future version of CCleaner could take care of that too! :)

Looks just like NASA WorldWind. :)

Similar, but much smaller download. And much clearer when you zoom in on big cities.

P.S. it can also be downloaded from MajorGeeks when the Google download site is closed.