http://lifehacker.com/5399564/five-best-an...us-applications
The ones that made it into the top five for voting are : Avast!, Microsoft Security Essentials, Avira AntiVir, ESET Nod32 and AVG.
What did you vote for? I went with Avast! because that's what I've been using for a bit. Thinking of moving over to Microsoft Security Essentials, but not sure how much more powerful it is (haven't read much about it)