The Best Just Got Better (fre Prog)
 

http://free.grisoft.com/doc/2/lng/us/tpl/v5

Not sure if you use it, but I think its great.

AVG Free Edition is the well-known anti-virus protection tool. AVG Free is available free-of-charge to home users for the life of the product! Rapid virus database updates are available for the lifetime of the product, thereby providing the high-level of detection capability that millions of users around the world trust to protect their computers. AVG Free is easy-to-use and will not slow your system down (low system resource requirements).

Highlights include:

Automatic update functionality
The AVG Resident Shield, which provides real-time protection as files are opened and programs are run
The AVG E-mail Scanner, which protects your e-mail
The AVG On-Demand Scanner, which allows the user to perform scheduled and manual tests
Free Virus Database Updates for the lifetime of the product
AVG Virus Vault for safe handling of infected files
Great customer satisfaction!
Please note that any previous version of AVG Free will be un-installed automatically during the installation of the new AVG Free.