Best Virus Checker

Well assuming you already have all the usual free ones, AVG etc, the best I found, and by that I mean the one that could find the bloody virus and get rid of it was
NOD32.
You can get a free trial here, I think I had to download it from work and run it from a memory stick my home computer was so screwed..

It was so good I actually subscribed to it for money and I rarely do that.  But if you have had the headache of your computer not working you will gladly pay not to sort it out again

Since installing it I have had not one virus despite many attempts by people hooking up infected drives to my computer