Comodo Firewall Pro - The Free Personal Firewall

Comodo Firewall Pro (CFP) is a freeware firewall that provides protection on a Microsoft Windows operating system from both inbound and outbound attacks. 2007 version 2.4.18.184 was rated amongst the best Windows personal firewalls with the highest score when configured at its highest security settings.

Version 3.0 is released since 22nd Nov. 2007
includes HIPS (Host Intrusion Prevention System) technology, to protect a computer from unknown attacks.

This brilliant piece of software provides the expert with all the insight you ever wanted, but is also very easy to use for the average PC User.

And now comes the best part of all:

It's Free. Forever. No Catch. No Kidding. Free for Commercial Use!

http://www.personalfirewall.comodo.com/

Redl's conclusion:
It is simply the best way to protect your Windows PC - except using Ubuntu Linux instead! ;-)

The book "The Best Damn Firewall Book Period" is essential reading for anyone wanting to protect Internet-connected computers from unauthorized access.