I love google Earth! I think it is the most interesting piece of freeware out there for folks to play with. The satellite imagery is very cool, and I've used it personally to check out my old hometown, map cycling routes and plan holiday activities.
Now, the good old folks at Google have come up with a lovely "Backyard Astronomer's Add-on" for their popular Google Earth application. "Google Sky" gives you a photo-real view of the heavens, with quite good detail surrounding star clusters, galaxies, constellations etc. It also provides real planetary and moon motion, and a tour of the universe using 1Hubble's photos. You start of with a "human eye" view and then can zoom into a detail, photo-realistic view as you please (see the detailed photo of the Double Cluster below for a nice example).
Check it out at http://earth.google.com and download it - FREE!