Just downloaded Version 1.4 of NASA's World Wind global browser and must say that it's a fine competitor to Google Earth. Much better user interface and controls; amazing amount of layers and real-time data. Can't support .kml/.kmz stuff, but still pretty amazing. Edit: I was wrong about importing Google Earth files (.kml/kmz); it can import them. Cool!I use Google Earth Plus (paid version) and think I'll be going back and forth between it and WW a lot.
http://worldwind.arc.nasa.gov/index.html