I work for a PC repair company, most of the virus infested PC's that come in have Norton products installed. I need not say more...
I too recommend Avast. I have run it across my whole company for six months now and not a single virus has made it through. When you consider we place approx 6-12 infested machines on our network a day, it is a good testament. The boot time scan is most excellent for already infested machines.