Bind named uses port 53 on both tcp and udp protocols, so you need to enter these iptable rules:
-A RH-Firewall-1-INPUT -s 0.0.0.0/0 -d 0.0.0.0/0 -p tcp --sport 53 -j ACCEPT -i eth0
-A RH-Firewall-1-INPUT -s 0.0.0.0/0 -d 0.0.0.0/0 -p udp --sport 53 -j ACCEPT -i eth0
-A RH-Firewall-1-INPUT -s 0.0.0.0/0 -d 0.0.0.0/0 -p tcp --dport 53 -j ACCEPT -i eth0
-A RH-Firewall-1-INPUT -s 0.0.0.0/0 -d 0.0.0.0/0 -p udp --dport 53 -j ACCEPT -i eth0


The "RH-Firewall-1-INPUT" part will change depending on your linux distribution and issue. Just have this string match the other rules preexisting in your /etc/sysconfig/iptables file.