These resources provide further information on iptables/netfiter or are otherwise a resource for use while administering a firewall.
Netfilter/IPTables Home
http://www.netfilter.org/
RFC 1918 - Address Allocation for Private Internets
http://www.faqs.org/rfcs/rfc1918.html
IANA Assigned Port Numbers
http://www.iana.org/assignments/port-numbers
Ports for Internet Services - another port list
http://www.chebucto.ns.ca/~rakerman/port-table.html
Practically Networked's Special Port List - useful for port forwarding
http://www.practicallynetworked.com/sharing/app_port_list.htm
Oskar Andreasson's IP-Tables Tutorial
http://iptables-tutorial.frozentux.net/
Linux IP Masquerade HOWTO
http://www.tldp.org/HOWTO/IP-Masquerade-HOWTO/index.html
Firewalling with netfilter/iptables
http://www.knowplace.org/netfilter/
Fireparse - Firewall log parser
http://aaron.marasco.com/linux.html
http://freshmeat.net/releases/47719/
IPTables Firewall Scripts and Configuration Files
http://www.malibyte.net/iptables/scripts/fwscripts.html
IPTables Connection Tracking
http://www.cs.princeton.edu/~jns/security/iptables/iptables_conntrack.html
Configuring NFS under Linux for Firewall control
http://www.lowth.com/LinWiz/nfs_help.html