is one of my favorite programs because it lists all the running processes on my Windows platform and the local TCP/IP ports they are bound to!
This program is more for technical people as most users don't find themselves needing to see TCP/IP port that a process is bound to. In my case I use Eclipse to develop Android applications, and it's useful for me to see which port a related process is bound to for debugging purposes.
Currports also tells me the path of the running process so I can easily locate which executable is responsible for which process.
I am using Windows version of this program, but it may be available on other platforms such as Unix and Apple OS.