If you're looking for information on security, unSpawn has a terrific collection of links in the first thread of the LQO Security forum. I strongly suggest a read.
It looks like your rules are right. Port 113 should be shut down quite nicely (although you might have a search around here about port 113 since there are some opinions on whether you should DROP or REJECT this port).
In my opinion, there are no good or bad ports....It all depends on what you want from your machine. I've really got only ssh and ftp running and ftp is locked down to my LAN only. You should also have a look at the startup scripts in your /etc/rc.d directory and comment out any services that you don't use. A port is well and truly closed if there is nothing listening. For checking for open ports, you could try nmap.
Finally, Simply Linux
has a section on security that is worth a look.