Lots of good apps already mentioned in this thread. I personally like the combination of Eset AV and Comodo Internet Security (just for the firewall). Both of these perform well (both individually and together) and are light on system resources. (Comodo Internet Security also has an anti virus component which I don't use and am skeptical of, however, it recently received a good review, fwimbw.)
But for a simple all in one integrated "suite" type solution, Eset Smart Security is getting better and better as it gets more mature. However, neither of the Eset products are free, unfortunately. But they do offer a 30 day free trial.