Stellarium is a really nice piece of cross-platform astronomy software released under the GNU General Public License. It discards the complex controls usually associated with such software and is perfect for wannabe amateur-astronomer laypeople like me to locate objects in the night sky.
The rear window of my flat has a southeasterly view over the North Sea, and I was able to use the software to locate both Jupiter and Saturn as they made an appearance through the window over the course of the evening. Through my recently acquired small refractor telescope, I was amazed to see Jupiter's major moons and Saturns rings, which is something I never thought possible using a small scope.
OS X users may be disappointed by the fact that Stellarium runs full screen and doesn't use Aqua, but it's still a very nice looking piece of software as it uses OpenGL to render its graphics. Also, the OS X version has a rather nasty icon, so I made one myself which is presented above (PNG version).