Digging around for information on Google Earth, I ran across the EarthSLOT project:
EarthSLOT is a collection of 3D GIS and terrain visualization applications designed to allow scientists, resource managers, educators, and the public better understand our planet and the earth science that goes on here....
Our mission at EarthSLOT is to advance earth science and earth science education through the use of on-line 3D terrain visualization and GIS tools. This technology is improving at a rapid pace, as more 3D engines come on-line and more developers begin using them. What seems to be lacking in the community right now is a site that hosts applications from various engines, reviews the technology, and discusses their strengths and weakness in regards to earth science and earth science education. Our goal, therefore, is to serve as this repository and forum for 3D applications that advance earth science and earth science education using any 3D software engines.
Mike Nolan also has a good overview of some 3D geospatial engines, including Google Earth.