Free Anti-Virus Guard
The AVG Anti-Virus is a free and one of the top ten antivirus for personal use and let’s you download the latest updates for free as well. I’ve read reviews which recommend AVG over the bloated Symantec anti-virus guards. I know what I will be using at home, you too can download AVG from here.
Edited (27-Feb-09) to update the download link, you should be able to see the download button off that link.