Microsoft WorldWide Telescope
Call me speechless.
I finally got around to downloading this software. It is absolutely amazing. The images are stunning, and the UI is so intuitive. I could stay up all night, gazing into the heavens, er, my laptop screen.
If you haven't seen it, go download it today. http://www.worldwidetelescope.org
If you're a fan of the night sky, you'll find it breathtaking.