I have an OEM of PC-cillen. Came with my Asus motherboard and it has been good to me. Includes a firewall.
Also, I went to trendmicro's web site and used their online scan feature for another PC of mine. It found a 5 viruses/trojans and quite a bit of spyware. AVG, Adaware, and Spybot combined missed these items. So, I'm left with the impression that PC-cillen is pretty good. They are very prompt with their updated definitions too. Sometimes 2 or 3 times a day even.
I think Norton is good too, but it makes my system somewhat sluggish by comparison to PC-cillen.