Microsoft Security Essentials

This is a free antivirus offered by Microsoft, a fairly new product, but is already getting a good response both from users and experts.

Microsoft Security Essentials offers protection from various types of malwares, along with antirootkit, and antispyware protection. The detection rate is quite good, with very little false positives. The Rootkit detection rate is very high. Microsoft Security Essentials is quite light on resources, and integrates well with Windows. The interface is very easy to use, with easy to understand settings, making it a good choice for average users.

The updates are integrated with Windows updates, which might be a disadvantage, if you like to keep Windows updates off.