Joe, how about using a Python script to parse your W3SVC1 logs? They are usually located at C:/WINDOWS/system32/LogFiles/W3SVC1 on the machine. Your script could run once per day, once per week, etc. as a scheduled task. I do this daily to parse out GET requests for requests to a particular web application and I record the requester IP along with the size of the response, the return code, and the client application making the request. You could also parse the logs for POST requests if you need to capture more. One the data is parsed, you can write it to a log file or insert the data into a database for reporting and record keeping purposes. Maybe a solution like this is a bit too custom for your liking, but you may already have the tools you need to do this without buying a COTS solution.
EDIT: W3SVC1 logs are those for the Default Website #1 in IIS. W3SVC2 would be for the next website created, should one exist, and so forth.
