The latest version of Google Earth (4.2) includes a feature that they they have been promising for a while, called Sky View. It is an awesome astronomy resource which allows you to navigate the universe, as well as the Earth. It is still Google Earth as you know it, but with a little button that allows you to switch from a view of the Earth to a view of the sky. The Sky View feature includes constellation labels, images and information from the Hubble Telescope, star names, and animated planetary orbits. Watch a video demonstration here. Or better yet, to experience it yourself, download it here.