ProcNetMonitor is the free tool to monitor the network activity of all running process in the system. It displays all open network ports (TCP/UDP) and active network connections for each process. It has advanced color based auto analysis system to make it easy to distinguish network oriented processes from others with just one glance at the list.
In the newer version 2.6, ProcNetMonitor by default displays only network oriented processes which make it easy for the user. Also user can easily toggle between network oriented and all running processes by just clicking on the check box. Also it presents improved user interface compared to previous version.
For more information and download, visit the main page of ProcNetMonitor