Here's a neat website that lists more than 450 freewares to do almost everything you ever needed. Some examples are - Removing Viruses, Firewall, Writing CD/DVDs, playing a CD, browsing the internet, screen capturing, (de)compressing file(s), voice of IP (aka. Internet Telephony) and many more..
Taking a step back, its quite amazing to see that there's a freeware to do almost everything you need on your PC. I am now waiting to find a similiar list for non-PC platforms like Mac.
And if you are someone who uses UNIX/Linux or something similar at work and miss the command line utilities at home, then head over to the open source GNU Win32 project that has Windows ports (non techies, read that as windows equivalents) for a lot of the commands. Some popular examples are:
and so on. See the whole list here.