I use AVG Free, with a scheduled run performed every day while I am at work.

I couple this defense with a Zonelabs ZoneAlarm Firewall, ewido, Spyware Blaster, and Spybot, all run automatically while I am at work, so when I come home, I am given audience to another barrage of messages telling me I am completely malware free.

And then I pirate the internet once more.