TCPView

TCPView is a Windows program that will show you detailed listings of all TCP and UDP endpoints on your system, including the local and remote addresses and state of TCP connections. On Windows NT, 2000 and XP TCPView also reports the name of the process that owns the endpoint. TCPView provides a more informative and conveniently presented subset of the Netstat program that ships with Windows. The TCPView download includes Tcpvcon, a command-line version with the same functionality.
TCPView works on Windows NT/2000/XP and Windows 98/Me. You can use TCPView on Windows 95 if you get the Windows 95 Winsock 2 Update from Microsoft.