"Microsoft Security Essentials"
is now free for download at:
http://www.microsoft.com/security_essentials/resources.aspx
I've been happy with AVG free anti-virus and Spybot Search & Destroy anti-spyware. But I've decided to try Microsoft's security suite. I'm hoping it has the registry cleaner that used to be included with Microsoft Onecare.
Not much more to say about it. It's from Microsoft, it's free, so it can protect all of your computers. Even the ones in the closet you don't use anymore.