UPDATE: ClamWin is no longer recommended by CS.  Lack of new features, and old interface now makes us recommend panda cloud antivirus or AVG.

I found this software awhile ago and haven't looked back. Not only is it free but it doesn't take up a lot of resources like the home verisons of mcafee or norton. I found that it protects just as good as those pieces of software without all the bloating fuss. Its made form the popular linux antivirus software called clamAV. It specific feature include scanning scheduler, automatic virus database updates, atandalone virus scanner, integration to MS Windows Explorer, and add-in to MS Outlook.

Check it out here