Surprisingly done a search and noticed that no one has ever posted it so ahh well.
Anyway Avast Antivirus completly free, very easy to use updates all the time and all that you have to do is,
1. Goto Avast.com
2. Goto Download then Select Programs
3. Select Avast 4 Home Edition which is free.
4. Scroll Down and select the mirror download site and download will automatically
5. When setting it up enter your email address as they will email your serial key so you can update, as it only comes with a 1 month key normally but when serial is entered it will go up a year or 2.
(you can skip points 1,2 and 3 if you use direct link)
Well thats it, they update all the time and won several awards, they would rather you would use the home edition for your personal computers as they don't like people using companys using the free version as then they make no money.http://www.avast.com/eng/download-avast-home.html