|The following freebie AV's get good reports around here:|
Microsoft Security Essentials.
Personally I found AVG a bit bulky. I've also seen Avira mentioned from time to time.
McAfee and Norton appear to get bad press (probably even bulkier than AVG).
There are reviews around but they vary from time to time, although the ones I've mentioned usually appear at or near the top of the list. There is a lot of personal preference of-course but I think it's fair to say that at any given time there will be viruses that some detect and others don't.
Often you don't really get a whole heap more by paying for an AV.
Other folk may have different views to those given.
As you probably already know, it is bad practice to have more than one AV working in the background. They can clash and cause issues.
We all live on a ball.