I tried most of 'em (Norton, PC Labs, McAfee)...

I finally wound up with Spy Sweeper with Virus Checker, which is head and shoulders above anything else I tried.  Unlike some of them, you can actually turn it off when your not on the web, and the settings actually work- if you set it to only check for updates manually, it doesn't still go out and check for them anyway.  Some of the others are EXTREAMLY aggressive on doing what they want to do, as if the only thing your computer exists is to run anti-virus programs.

It also cleaned out a really bad virus which the others coundn't touch.

You have to buy it though, it isn't free, but it is pretty cheap.