I use Avast! antivirus. It's free and I think it's one of the better ones anyway.
McAffee and Norton are always overly strict, complaining about stupid stuff like Internet Explorer trying to access the Internet. Yes I know it's trying to access the Internet...I'm the one trying to access it. I also find them more resource demanding than Avast!.
Plus, Avast! has a pirate voice setting. You can't go wrong with that.