Comodo has come out of nowhere from what I can tell to put out some fairly nice security applications. One of which is their free firewall. It is sort of annoying that the program updates of of nowhere, but it still seems to provide some great software firewall features.

Kerio Personal Firewall was bought out by Sunbelt a while back. It has been able to keep up one of the best free software firewalls around and has held onto the top rated free firewall spot for several years. I have stopped using it personally, but it still has some advantages for those looking for a great free firewall.