Best antivirus for windows 7 ultimate free download

AVG is good and free. Avast is free for 30 days.

Avira also it's great and free

I use avast and it is free.

I like MSE, Microsoft Security Essentials....

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  

I like Unthreat Antivirus, it's free and easy to use. Haven't had a virus since I downloaded it!