pfSense is a slick little firewall OS based on FreeBSD. I have used it on and off for a few years now, and I’ve been very happy with it. Internally it uses the highly-regarded pf (originally from OpenBSD) for its firewalling.
If you have an old machine lying around, make sure that you have at least two NICs and give pfSense a try. It’s fairly intuitive and very powerful. It can handle a number of other tasks for your home network right out of the box: DHCP, DNS, NAT, NTP. It can act as a VPN. It’s accessible via SNMP, and it keeps some great usage statistics. Add another NIC and you can have your own DMZ at home.
Oh, and it can do hot failover. Like I said, slick.