If you have multiple application pools started in IIS 7 and you want to determine which w3wp.exe process to attach the Microsoft Visual Studio 2010 debugger to, you can use the Microsoft Windows Task Manager.
Start the Microsoft Windows Task Manager: press [Ctrl + Shift + Esc].
Add the columns "PID" and "Command Line" to the Process tab.
The name of the application pool will be shown in the Command Line Column.
In this case the WCF service I wanted to debug, was running on the default [ASP.NET v4.0] application pool.
The Microsoft Windows Task Manager, shows the PID of this w3wp.exe processes as 8188, so now I can attach the Microsoft Visual Studio debugger, to the process with ID 8188, to start debugging the WCF service