Sophos offers Free Anti-Virus Home Edition for Mac
I've been using ClamXAV but it's a pain. Hopefully this will fill the void for free Mac OS X virus software. I'm gonna give it a shot on a couple of my machines. It supports both PowerPC and Intel by the way. No mention of email support etc. though as far as I can see, but I haven't yet installed it to do a full assessment. I just hope it's not as much of a pain as ClamXAV.
BTW, it's rather amusing that the "Bad Things" directory has FlashPlayer in it.