Free Antivirus

AVG.	AVG is obviously trying to "hide" its free offer as much as possible on its website (same marketing strategy used by RealPlayer). Unaware users who can't find easily the free version on the web site often resign and buy the pro version, believing it's the only way to get the software. Otherwise, it's a very good antivirus.
ClamWin	Note: Open Source
AOL ActiveVirus Shield	Note: Kaspersky's engine. In the "free" world, I am personaly favoring AOL ActiveVirus Shield which I found both easy and effective
Avira AntiVir	Nagware
Avast! 4	Note: Highest Betanews's satisfaction score

This said, I am always trying to push relatives, friends and clients to buy a licence for NOD32, the best AV IMHO. All I convinced to buy NOD32 are very happy users, never to be bothered again by virus. (The only sidedown of NOD32 is the lack of inbuilt reregistration process. When the licence expires, NOD32 don't download updates but says nothing, Eset doesn't send a email reminder either and to get a new licence, the user has to buy an upgrade package on the web site. In other words, Eset is TOO much unintrusive! ).

---