Armchair astronomers and space freaks listen up! The amazing developers behind Stellarium have accomplished quite some amazing things. Used by many real planetariums for their projection showings, Stellarium is an amazing feat of open source software development, giving the user a realistic, 3D sky on a desktop environment, allowing users to enter coordinates, browse the night sky or even beam it onto your ceiling before going to sleep. The educational usage and possibilities of this is amazing and I for one am considering purchasing an HDTV projector simply to see Uranus on my ceiling at night!

Download: Stellarium - Open source planetarium for your computer