ClamAV works fine in OS X, Windows, Linux, Solaris, OS/2, and others. It's free. It is now owned by SourceFire, the people who make the firewall sniffer product, Snort. The product is available as source or as installable packages. See http://ClamAV.net/
I've been using it for years in a corporate environment with great success. No single AV product can do it all so you may wish to run more than one such tool.
A shoot-out of the major players in AV technology:
http://blog.untangle.com/?p=95
Last edited: Aug 17, 2007