My all time favourite computer defense/clean-up program has got to be CCleaner. Not really antivirus like what you're looking for, but it obliterates cookies, lots of spy/adware type things...pretty much everything that clogs up and slows down your computer. Best part is that after its first few sweeps, it only takes like 30 seconds to run...I run it 4-5 times a day.
http://www.ccleaner.com/
CCleaner + AVG + Spybot S&D + AdAware = All you'll ever need.