The only FREE firewall with 100% leak protection out of the box. This is a very good FREE firewall, and tested at the very top of the list in firewall leak test ratings. Have a look at http://www.matousec.com/projects/windows-personal-firewall-analysis/leak-tests-results.php#firewalls-ratings to see for yourselves the results as compared with the other "Big Boys".
I have been using Comodo Firewall, but after comparing it's score of 9475 against Online Armor Free's score of 9625, a perfect score, well, I've made the switch!
Sadly, this program is not suitable for Windows Vista.
If you are interested, you can get a copy at: http://www.online-armor.com/online_armor_free.html
Take some time and read the information presented... you may just start running a new firewall yourself! As always, thoughts and comments are welcome. :-)