I've heard recently that AVG is considering charging for their anti-virus software. They use the free version to convince commercial users to switch to their pay version. The results haven't been the best so the rumor is that the free days are coming to an end.
There is a new "free" one out there just in case. I've heard some good things about it. It's at
http://www.avast.com/. So if AVG does decide to charge you may want to keep this link handy.