CurrPorts (32-bit version)
Run the program, and it displays a list of every port currently open, and lists the process that opened each port, the full path of the port, version information about the process, such as its product name, the time the process was created, and the user who opened it. In addition, it marks in pink any ports the program deems as suspicious. You can then kill the process that opened the port.
If you're not a techie, you most likely won't know what to make of CurrPorts. If you are, you'll revel in it.