We really don't recommend many apps in the way of virus protections as Macs, while susceptible to malware (see Thomas Reed's Mac Malware Guide), has no known viruses.
Thomas has done some some extensive testing of av/malware software, however, and you can see the latest results here. Of the 'top three' malware detection packages, the only I have used and can therefore recommend is Sophos for Mac. I've been testing it for over two months now but have never had it flag any file. But it won't do any harm to your Mac, unlike some of the commercial products out there.
So if you feel safer using av software, give Sophos a try. You really don't need it, though, as OS X and thoughtful downloading should prevent any malware from affecting your computer.