For Anti virus --- NOD32 from ESET, not free but small footprint very configurable. I ended up with this after putting Norton 2005 on my girlfriends old laptop and watching it grind to a halt. After seeing it slow that machine down so much I figured may as well remove Norton from my work PC and use something that's more efficient. NOD 32 also has the advantage of not being the target for every virus writer on the planet. On other less important machines, I have installed AVG the free version it seems very effective but has a larger footprint than NOD32 hence I don't use it on my Work PC.
Spyware --- Spybot search and Destroy and Ad-Aware personal. I consider spyware and browser hijackers more of a problem now than viruses.
Other --- dropped Microsoft outlook and don't use MS Internet explorer (much) now using Firefox and Thunderbird. "enable performance email" does not work with Thunderbird, which is pity because SolidWorks doesn't get to hear about my crashes!!
For a firewall --- I have a firewall built in to my DSL Router + Windows own firewall. I used to run Zonealarm pro for several years but it never once had to stop an intrusion, probably because of my hardware firewall. Zonealarm is also a preferred target of virus writers, hence Zonealarm is constantly issuing updates and patches.
John Layne