I had never heard of Avira until I started Googling for anti-virus reviews. A recent test by AV-Test.org for PC World shows Avira detecting most viruses in the PC World review.
For home use they have a Free personal edition, which is scanning my computer as I write this. Some of the features described in the review are not included in the free version but I looks great. At last an anti-virus program where you can still select some options, such as excluding files from the scan, If you want to. You can even enter an SMTP server + e-mail address to mail detected threats.
A minor issue : the windows are not resizable
Update Feb 2, 2013:
It's still free, but I like the software so I paid for the Avira Antivirus Premium. I wasn't missing anything in the free version. I just wanted to pay for the software I have been using for more than 2 years now.