BitDefender 10 Free

Get this. NOW.

http://www.bitdefender.com/

This has got to be the most feature-packed free AV software on the net. Period. It has hourly automatic updates, a scan scheduler, and it works wonders. It was the only program that found a nasty little keylogger that was lurking on here (going against NOD32, avast!, SUPERAntiSpyware, Ad-Aware...) and is overall a great AV scanner. Do yourself a favor, and download it.

I have always used bitdefender (or kaspersky when bitdefender didn't work). I just love it :)
there is a newer version too :) the 2008 version.. I got it, and it is better because it is silent. No more interrupting when you play or watch a movie.. it even has a game mode, when it shuts down all scanning while you play, to allow better gameplay.