AVG will no longer be free in 2007. I used to have it, but for the past couple of months, after an update, I got popups asking me to purchase their upcoming new version. Pity, as it was one of the better anti-virus programs besides also being free.
There are a few free online scanners though. PandaSoft and TrendMicro are two of the bigger ones I know of that offer a free online scan. And unlike the online scanner from McAfee, the ones from PandaSoft and TrendMicro actually remove stuff instead of just listing what virii you have and asking that you purchase the software.