The best anti-malware for any platform is between the chair and the keyboard. This trojan, for example, is an IM or e-mail purportedly from a friend; it then points to a fake YouTube video, actually a Java applet, which then requires an admin password to install. It’s what hackers call “social engineering.”
That said, ClamXav is free, robust, free, frequently updated, and free. I run it every few months just to make sure I haven’t picked up a Windows virus I might unwittingly pass on. It has yet to find anything.
Thanks for the replies...yes, I’m usually alert for any funny stuff that could be a security risk, but I’m not invulnerable, just an average user. So I have Intego VirusBarrier X6 for any kind of malware...and it includes a firewall that I can understand a little better than the options that are given in the OS X firewall.