I'm using Avira (the free version). You can set a local security policy to stop the pop up if it annoys you.
The latest Symantec is supposed to be pretty lightweight now and some fairly good detection rates too.
If you're looking for some
independent comparisons of AV products, check out
AV Comparatives. They do regular reviews of the popular AV products and give information on the speed, detection rate and false positives of many of the top AV products out there.
I like to consider myself fairly computer savvy but I don't think I'd EVER run without an AV product. That's just asking for trouble. Besides...if you don't run an antivirus, how do you
truly know you don't have a virus?