AVG has been having problems recently. They uploaded a bad signature file for the 64-Bit version of Windows 7 which causes a the system with AVG installed to constantly crash and require a reboot. This is in addition to problems they've had a year or so ago with Windows Vista. As a company, they have fallen from grace, and I think a lot of their success is them resting on their past achievements.
I second Microsoft Security Essentials. I've been using it for about a year now and it's installed on two PCs in my home. It's basic, but it does it's job, it's light on system resources and there is NO paid for version. It is what it is, and you get it free with nobody from Microsoft trying to sell you the paid for version, ever.