M0n0wall is an open source firewall and wireless router

NewsForge | For network security, build a m0n0wall
Just read about this, built on freebsd it looks like a tight, fast secure solution for anyone trying to protect a network.

M0n0wall is an open source firewall and wireless router developed by Manuel Kasper, built on a stripped-down FreeBSD operating system. M0n0wall offers many of the same features found in commercial firewalls products such as Check Point Firewall-1 and Cisco Pix, including stateful packet filtering. With it you can create a secure virtual private network (VPN) between two sites, or you can use m0n0wall as a VPN gateway, so you can access your LAN secure from the Internet. You can use RADIUS for client authentication in order to raise the security even higher.