The only problem I have with Norton Antivirus is that it is hard to *JUST* get Norton Antivirus by itself.
It normally comes with Norton Internet Security, Norton 360, or whatever the bundle of the month is, costing the same or less than NAV by itself. All that crud running at the same time is what slows a gaming system down terribly, and NAV gets a bum rap.
I pretty much get all the major AV vendors software for free, being a professional reviewer, and NAV running by itself is not any more of a resource hog than anything else in my tests, and it has a pretty good interface and a bunch of serious people backing it.
Now then.
If you don't want to pay for another av product, then I recommend AVG Free (free.grisoft.com). It gets updates reliably and regularly, is resource friendly, and the automatic scanner can be manually disabled during gaming. Also free is AntiVir from
http://www.free-av.com/. It does well on those german tests, and so far it seems pretty OK to me. One problem is that it periodically displays a nag-screen encouraging you to buy the full version - this is disable-able with instructions at
http://www.elitekiller.com/files/disable_antivir_nag.htm, but should you really have to do that? I dunno.
As for commercial options other than NAV, Kaspersky and NOD32 are both excellent. I lean towards Kaspersky.
-Warr