Comment firehol (Score 3, Interesting) 187
I'm a little surprised nobody has mentioned firehol - http://firehol.org/. I've been using it for my simple needs, and it is fabulous. Easy to learn, simple language, great results, and CLI-friendly. (Prior to discovering it, I used guarddog, which I found to be good but which isn't anywhere near as good as firehol.) From the firehol page:
FireHOL is an iptables firewall generator producing stateful iptables packet filtering firewalls, on Linux hosts and routers with any number of network interfaces, any number of routes, any number of services served, any number of complexity between variations of the services (including positive and negative expressions).