No A/V protection is perfect - I switched us from a corporate Sophos deployment to MS Security Essentials purely because it found (and almost as importantly effectively removed) a couple of bugs that Sophos was struggling with. Since then (2010) it has served my office well and my home use has been easy-going too, though it did need a manual scan to find and remove some java exploits this week (thanks for that MineCraft - encourage teenagers to avidly click everywhere for l33t MineCraft mods written in the most insecure programming environment possible...)
Security Essentials is free for home use, really fast and fantastically lacking in bloat - worth a look
There is a big list, as above comments all are good. I personally use escan as it the best so far according to me. It gives my computer as well as android phone a complete security and make sure that the speed never gets slow down.
Don't bother using anything but Microsoft Security Essentials. Most programs suck up a huge portion of your processing power for almost no reason. I've been running this since it came out and I've never had a virus. http://windows.microsoft.com/en-us/windows/security-ess... I've always had problems with other antivirus programs such as Avg, Norton and Avast.