Don't let the name fool you, Comodo Firewall Pro is one of the best freeware programs around that can also hold its own against other pay firewalls. Previous user complaints about resource hogging and a confusing interface have been addressed and this application has never been easier to use.
It still provides a smorgasbord of information and options for advanced users, but it's simple enough for beginners, and runs smoothly and silently in the background. When you first install it, the Comodo pop-ups come often as the program "learns" your online behavior, but those soon stop. Summary, Firewall, Defense +, and Miscellaneous tabs provide links to relevant security issues so users can drill down to learn more about how the firewall is performing and what exactly it's doing. The Host Intrusion Prevention System supposedly protects against unknown threats--obviously, it's hard to tell if it works unless an unknown threat gets in, but it didn't seem to affect system performance negatively.