I use IPCOP on all my border routers at my client sites ... with the openvpn plugin. CentOS can certainly also be a router if you set it up that way, but I normally use IPCOP.
I don't think there are many tools that are going to make management as easy as it is on IPcop ... though, there has not been much website activity there lately.
There is a new patch in beta right now. 1.4.11 I think. I guess a firewall has so little software on it that security updates just seem to be farther apart. Less exposure = less vulnerability. I mentioned Clarkconnect as an alternative to trying to use CentOS since it is based from CentOS 4.
personally i really like www.smoothwall.org as its super easy to setup and performs well. Its also a really active project.