Smoothwall is supposed to be the best...
The authors claims no one has successfully hacked their VA Linux Distro with Smoothwall running on it. I from personal experience have been using it at home over a year now, it's great. I tossed the Linksys, which is junk in the trash, not a reliable "firewall" solution.
No frills, or unneeded extra services, suspectible to hacking on their firewall, but pretty easy to use once you read the Manual.
Check it out at: smoothwall.org
Aaron