Need advise for a linux firewall

Looking for advise on setting up a linux based dedicated firewall. Apparently, there are plenty: http://en.wikipedia.org/wiki/List_of_router_or_firewall_distributions I'm looking to have the firewall sit in front of a public network of windows boxes. Also, would want to be able to load-balance and re-shape traffic inside the network. I was hoping to accomplish this using iptables, but if anyone has any other suggestion, I'd love to hear it. Thanks! Abdul Nazeer