Many a times you need to find what are the ports which are open and connected to Internet i.e. for example like yahoo meseenger or gtalk always connect to their server using a particular port on your computer.
APort is neat utility that can give you a lit of programs which are using a port and connected to a particular ip address. It gives a nice interface with details of process, hostname etc. Since process can change and new can start, the list gets updated every few seconds.
Hwoever if you would not like to install a software for this purpose, you can use the command line option for this which is netstat -nabv 5. You will need admin privilege to run both of them.