I use McAfee and have loved it. Both the firewall and virus protection are near idiot proof to use, and other than having to re-install the virus protection on the rare occasion when an update doesn't load right, I've had no problems at all. I could have Norton for free from work, but choose to pay for McAfee. I'm about as cheap a bastard as you'll find, so that's saying something.

I also recommend Ad-Aware and SpyBot Search & Destroy for control of adware and spyware. I use both of them, and have been very happy with them. Plus, they are free!

Also, Pop-up Stopper! Pop-ups suck, and not in a good way.