I am avid amateur astronomer, so imagine my delight when those clever people at Microsoft released Worldwide Telescope, free, yesterday. WWT turns your pc into a planetarium, and its pretty amazing. I spent a great deal of time mucking around in it last night. The effort that has gone in and the data that is available to it is phenomenal. Really great when its 2 degrees outside and you don't really feel like setting up your telescope with frozen fingers.
The software is free and can be downloaded from
http://www.worldwidetelescope.org/