I use zonalarm. It monitors all malicious traffic incoming and outgoing at all times and also has an anti-virus scan.
Haven't had any problems/viruses since my install a year ago
zone alarm has an anti-virus feature that uses your current installed anti-virus client. Afaik, it doesnt have a build in anti-virus client, but correct me if im wrong.
I personally use Symantec Anti-virus, v9. I've just installed v10, and while its pretty good, im having some minor difficulties. Not sure of all the other anti-virus clients out there, AVG seems popular.