Astronomy Software and Tools

Here's some pointers to astronomy software and tools you can get on the Internet, that I think are noteworthy or useful. They are all Free.

Constellations and Deep Sky

SFA Star Charts: Printable star charts, in Adobe Acrobat format. These are excellent for learning the constellations.
Night Vision for Java: Basic star charting software, suitable for beginners and those who want a good, simple star chart program. Best of all, it will run on just about any computer system — Windows, Macintosh OS 9 or X, or Linux. You will need a recent version of Java installed.
Cartes du Ciel (Sky Charts): This software is Windows-only, but it is a very well regarded sky charting program. This package is full-featured and has a very deep database of celestial objects.
Utah Skies Messier Telrad Finder Charts: If you're observing the Messier objects with your telescope, here's a great set of charts to help you locate them. You can buy commercial versions of these charts, but these are Free.

Solar System Live: This online Solar System orrery (works with any web browser) will draw overhead maps of the Solar System, allowing you to see how the planets are positioned with respect to one another and the Earth.
Celestia Space Simulator: If your computer (Windows, Mac OS X, Linux) can display 3D graphics, this is an excellent real-time space simulator. Imagine you have a spacecraft and can fly through space viewing the solar system and the Milky Way.
Meridian: This software (Windows only) is very useful for observing the planets. It will show you what side of a planet is currently facing you, whether you can see the Great Red Spot on Jupiter, where the moons of the planets can be found, and much more.

Virtual Moon Atlas: This program (Windows only) will display a Moon map onscreen, so you can identify craters and other surface features. Incredibly detailed, with lots of information. Works best with 3D-capable computers, but not required. I use it on an old 300Mhz laptop without 3D acceleration, and it works fine. You do need about 100 MB of disk space for the full version, though.
Photographic Moon Book: Here is an online book about observing and photographing the Moon, in Adobe Acrobat format. This guidebook contains a series of photographic maps of the lunar surface. Together with a good lunar atlas (such as Virtual Moon Atlas above), it is a great way to learn the Moon. I burned the files to CD, took them to Kinko's (a copy and print store in the United States) and had them print and bind a full-fledged book. Note for Americans: if you do this, note that the book is formatted for A4-sized paper (metric sized) and you will need to have Acrobat shrink the pages slightly for printing on U.S. 8.5 by 11-inch paper.