NSS will fit the bill for those looking for a good quality on demand only AV. It won't interfere with other AV/AM. I have AntiVir Premium as well as SAS Pro and Mamutu installed, and they all get along just fine. It will not load persistent processes, and you can update virus defs at will. You do need to install the Google Pack (http://pack.google.com/intl/en/pack_installer.html?hl=en&gl=us) to download it. However, GP itself can be uninstalled leaving NSS to do its thing. NSS does have its own uninistaller if you find that you don't like it. Just a friendly heads up!