We were gettign an error with one of our WCF services "System.ServiceModel.CommunicationException: An error occurred while receiving the HTTP response to..." and needed to get additional information on the problem.  Below are steps to use the built in diagnostics with WCF to find out more info for the error above as well as the overall health of your service.

1. Add to your web.config:
   
    <system.diagnostics>
       <sources>
         <source name="System.ServiceModel.MessageLogging">
           <listeners>
             <add name="messages"
             type="System.Diagnostics.XmlWriterTraceListener"
             initializeData="D:\LogFiles\SalesOrderTrackingService\messages.svclog" />
           </listeners>
         </source>
       </sources>
     </system.diagnostics>
   
   <system.serviceModel>
       <diagnostics>
         <messageLogging
              logEntireMessage="true"
              logMalformedMessages="false"
              logMessagesAtServiceLevel="true"
              logMessagesAtTransportLevel="false"
              maxMessagesToLog="3000"
              maxSizeOfMessageToLog="2000"/>
       </diagnostics>
   ...
   
2. Create the necessary folder and ensure the security is set so IIS/ASP.NET can write to the log file
   
3. Use the SvcTraceViewer.exe application to view your log file
   
   This tool can be found in the SDK directory...for me, this was C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin