Avira Antivir Personal Free Anti Virus is a great piece of security software that handles protecting basically all versions of Windows from viruses. It is very lightweight compared to commercial products like Symantec and even F-Prot, which I have both used in the past. The only draw back to this software is that it updates randomly each day, which could be a bit of a pain if you are busy doing something. Avira offers other security applications on their site, as well as commercial versions of their Antivir Anti Virus software.

Comodo has come out of nowhere from what I can tell to put out some fairly nice security applications. One of which is their free firewall. It is sort of annoying that the program updates of of nowhere, but it still seems to provide some great software firewall features.

Kerio Personal Firewall was bought out by Sunbelt a while back. It has been able to keep up one of the best free software firewalls around and has held onto the top rated free firewall spot for several years. I have stopped using it personally, but it still has some advantages for those looking for a great free firewall.