Mirapla Sky for Windows This is a free program that shows the sky as the naked eye observer would see it. Due to its high degree of realism and simplicity it is recommended for learning the constellations in conjunction with an Astronomy In Your Hands Star Wheel. (Windows)
Hallo Northern Sky Highly recommended as a free planetarium program. Despite the name it works anywhere in the world. You have to download several files and save them all into a new folder. You also have to know your latitude and longitude so that you can set it up properly. The best place to find your latitude and longitude is to visit Heavens Above. It is well worth the effort in setting it up as it is an excellent program. (Windows)
Starry Night - Highly recommended as a reasonably priced commercial planetarium program. (Windows and Mac versions)
Planet's Visibility This free program shows when the planets are visible in the night sky. An excellent aid to planet-spotting. (Windows)
More planetarium and related software - A comprehensive list of planetarium software for Windows, Mac, and more.