"Well Known" TCP and UDP ports used by Apple software products:
It's a good idea to know what's coming in and going out of your computer. Here is a handy list of ports and protocols that Apple software uses, just to keep you from freaking out when you see all sorts of weird connections on your log. Also, if your firewall is blocking this stuff and you're missing features (like Bonjour recognizing other Macs, you need to unblock the appropriate ports for your network.