Over the years I have tried, and eventually rejected just about every free Anti-Virus out there. All of them either do not detect important viruses, or they hog so many system resources that they will drag down even a top of the line computer. I also purchase Norton, and found that it slowed our computers down so much that I thought we were still using Windows 95!
Last year I tried what was then a new product,
VIPRE It has proven to be the best I have ever used. Since installing it, it has caught ever single virus that has come down the pike, and is super light on using system resources. In fact I just finished updating my subscription for another two years.
One "free" program/service that I could not be without is Gmail. I can access my email for any computer, everything is in one place, and with the large amount of storage Gmail offers, I rarely loose anything (unless it's because of my own stupidity)
I also agree with everyone who recommends FireFox.....with all the add-ons available, it makes life MUCH nicer that most other browsers.
I'm one of those people who is always looking for free programs that are useful. Every morning when going through my routine, part of it is to check PC World, and Download.com for useful free programs.
There is another site:
http://www.giveawayoftheday.com/ that gives away programs that would otherwise cost. Although most of isn't useful to me, every now and then they offer something that is very good.
Most notably for me have been SoThink DHTML menu (I use for my website), and Glary Utilities.