Well, Comodo Internet Security has a free version that I linked to, in my opinion the best security software that you can get for home computers. It has tons of configuration options, but that may be too much of a learning curve for most users. It's well worth it though imo.
People were questioning this company in the beginning cause they couldn't believe they could just deliver such an advanced security program for free, unless there is a catch. But they're doing it to increase their reputation and earn trust in their company, to make people buy some of their other security solutions.
I highly recommend people to try it out. They have a forum with lots of tips how to configure it for maximum security.
The firewall even has a Paranoid Mode you can switch too, but I haven't tried that myself. I think it's overkill that may cause too much problems with safe applications.