I wrote a simple VBScript that helps you identify TCP/UDP ports and their well known services.
Download port.vbs and place it anywhere in your system path.
To use it, enter port [portnumber] (i.e., port 389) and the script will display the well known service associated with the port, as shown above.
Alternatively, you can enter port [searchstring] and the script will show all ports that contain that search string. For example, port ldap will show all the ports with ldap in the service name.
The script works best from the command line when WScript is set to be your default script handler. Simply enter wscript from the command line to do this. Otherwise, you'll need to type cscript port [search] from the command line.
Update! See this post for the same script in Powershell.