Microsoft Research recently released its free World Wide Telescope application. The WorldWide Telescope draws on more than 12 terabytes of imagery from several orbiting and land-based telescopes. The desktop application downloads the images on demand and stitches them together to form an interactive, browsable universe supplemented with information from top astronomical databases.
It also allows the user to take “Guided Tours” that astronomers and others have put together. I thought it was pretty cool!
You can check it out at: http://www.worldwidetelescope.org/