http://www.stellarium.org/

One of the most useful pieces of astronomy related software. Download, install and run the program. Then enter the coordinates for where you live and the program uses your computer's clock to give you a view of the night sky from your position. Have a play around with the settings, it can show you the names of planets, stars, galaxies etc. You can zoom in on an object and zoom back out again. You can also go back and forward in time which is really helpful for planning what will be in a good imaging position at any particular time.

http://www.astronomie.be/registax/

I use this to align, stack and process the images I've taken with a webcam. There are plenty of Registax tutorials available on the web to get you started although I've done a step by step guide of exactly what I do with Registax to get results under my Image processing section. I only know the basics and get reasonable results.

http://www.stark-labs.com/phdguiding.html

I can't believe this program is free, it's amazing and so simple to use. If you have a motor driven computer controlled mount, an imaging scope & camera and a guide scope & camera then this program will keep your scope aimed at what you're imaging. You'll find other useful software on the site including Nebulosity which you can either download for a fee from their site or if you want your own CD copy you can contact Ian King Imaging on 01892 834004.

http://wcs.ruthner.at/index-en.php

Can be used when you want to polar align your scope and mount. You will need to have a guide camera linked to a PC to use this software. I found it quite confusing although there is a tutorial on the site and a forum that I used when I had questions. Many people to have great success with this program.

There is a simpler solution I used to polar align but I've lost the web link and can't remember the name. I'll add it to this list once I've found it.

http://www.astrosurf.com/astropc/qcam/programme.html

I use this program with my webcam for imaging. The link will take you to a French website. On that page you will see a link called English Documentation. Click on that for instructions.