There are lots of free anti-virus programs available and more becoming available all the time. AVG is considered pretty good but here are a few more that I am aware of.
http://www.avast.com/eng/av4_version_comp.html -- Avast! Free Anti-virus
http://www.clamwin.com/ Clam Win -- Free Open Source Anti-Virus
http://www.free-av.com/ AntiVir -- Free Anti-Virus