Lists of ports based on the applications using them
Here is a list of applications with their respective ports, available on the site portforward.com
http://portforward.com/cports.htm
Under Linux, if you want to know the ports reserved for the most used protocols, simply view the
/etc/services file.
For example:
Postfix a mail server application, makes uses of the
SMTP protocol.
Using the following command, you will get the port number associated with the SMTP protocol:
cat /etc/services | grep smtp