ASHISH65 :
Microsoft security essiantials is one best i have used among others due to simple display,updates regulary,less resource usage.
I agree with that completely, in windows 8 though it's called windows defender. Though prior to 8 windows defender was just an anti-spyware, MSE or microsoft security essentials was the full anti-everything.
Personally I use MSE + Windows firewall which is a good combo, though I have added MBAM or malwarebytes anti-malware pro which add realtime monitoring which is designed to work with anti-virus and not conflict with it (once you add an exception to the antivirus for MSE) and it has worked well. Though it mostly just blocks malicious websites for me and never had to block an actual threat, but it was cheap for a lifetime subscription and gives me added peace of mind so money well spent.
For me though it's hardware fire - windows firewall - MSE - MBAM for my security, that and I try not to do anything stupid online.
If for some reason you don't want to use MSE or a free one your internet provider probably gives you a free anti-virus suite, I know most do that now days. Though it seems like most people don't know about this or bother to check. I think my service gives me Norton or Mcafee though I had such bad experiences with them in the past I refuse to touch them now dispite hearing that they are no longer bloatware.