I can now personally vouch for NOD32, its great and absoloutley minimal on system recourses. It may look abit simple and uncustomizable, but it is in fact the best AV software around. I tested it myself against Avast, Kaspersky, Bitdefender, ZA Antivirus and a few more. It was just my personal choice and always comes out tops on the online virus ratings.
Problem is these days you NEED anti-spyware and a firewall too. So another app to check out would be Outpost Personal Firewall Pro. Better than ZA in my opinion.
Great for antispyware is Windows Defender, the new version of Microsofts antispyware. Problem is you have to have a genuine windows copy, no workaround or patch for it yet as far as I can tell. Otherwise i would be using that.