Proc Net Monitor is the FREE software to monitor & analyze the Network activity of all running Process on your system.
It shows all open network Ports (TCP/UDP) and active Network Connections for each process.
It also presents unique 'Port Finder' feature which makes it easy to search for particular Network Port used by any of the running processes. For example you can search for port 80 to find all processes who are accessing web (HTTP) services currently. You can right click on any process and perform more action such as killing it, viewing properties, performing scan etc.