I tried Panda TruPrevent personal 2005 to compliment my Nortons but did not like it. It is 32Mb and I had trouble with the taskbar icons which kept popping up endlessly and without any control, so I uninstalled and deleted it. It is shareware and on test for a month.
I would highly recommend AVG paid version. It is well worth the £20, and you get updates almost daily. It runs much the same as the original Free v6.0. It doesn't interfere much with games, unlike NIS, and McAfee which manage to make a game stutter. I don't think AVG have any yearly subs either, unlike the others.