Well, I've been using Kaspersky Anti-Virus for the last year or so.
It's not free, but not that highly-priced, either. The safeguard it produces is actually surprisingly good and there are new virus databases out almost every day, which (if not specified otherwise in the settings) will be downloaded automatically to the PC. The UI is pretty self-explanatory and the English version is more than understandable. In my hands it has worked better than Norton Antivirus 2002, which was my anti-virus earlier. It also has versions for both Linux distributions and PDAs, so the company hasn't really been standing doing nothing.
Because I've been using many different computers in Finland and hence used the anti-virus program as well, I can say I know F-Secure Internet Security 2005 pretty well (it's got a 85% penetration ratio over there, at least, since it ships with every broadband connection). Its anti-virus abilites are moderate (with a "Parts licensed from Kaspersky"- text in its About box) compared to Kaspersky, but it has a bit more cluttered UI (and some quite weird word choices in the original Finnish version) and versions for 'smartphones' using Symbian Series 60- operating system. The F-Secure- package rates higher than moderate on my list, but doesn't beat Kaspersky, at least not while I've been using those two.
It must be noted, though, that there were no false alerts or virus infections on my computer and on computers close to me while I've been using them. So they're both pretty good for Home Use. For business or larger networks with Linux servers serving them, though, I'd go for the Kaspersky Labs' offer, since they can offer a bit better defence, in my opinion (in that only, I have not run any real tests about the actual security they've produced).