AVG's got too flabby
I stayed with it for a long time. But when I realised that is uses 50-200 meg once loaded, and was covered in features I didn't use I figured it was time to change. I also started to get annoyed with not being able to turn of features such as auto update, without the icon going to alert.
I tried most of the ones I've seen mentioned around but had feature/performance/stability issues with most of them. (Minor, but still not perfect)
Then on a whim I treid PC Tools Antivirus. Pretty basic, but its got real time protection, heuristics, email scanning and all the other basic musts. From a cold start is sits in memory at about 5 meg, going up to 10 after a while (but no higher even after a couple of days)
I noticed it most on my rubbish laptop, which went from solw and dodgy, to useable instantly. I've changed about 7 or 8 PC's over to it now, and they all seem a little happier.