I'm running Avast Internet Security and I like it. The free Avast antivirus is good as well. It comes with email scanning in it and no nagware dialogs either.
Microsoft Security Essentials is good too.
You can't really go wrong with any of the choices given.
I see a post about best A/v on here almost daily. And there is this large pretty sticky up top with all the info in it already. We should just put a link to that anytime anyone asks.