I use Avast. Supposedly not the best out there, but definitely not the worst either. I can probably credit good browsing habits just as much (if not more) than the A/V as for having a good track record with me, but Avast is maintenance free and doesn't seem to get in the way of anything.
Norton used to be very good, but the last couple of versions I tried installing were so intrusive and had so many things running, it just wasn't worth it...