web service that I can use to test posting an xml document

I'm considering starting a project that will require me to post an XML document to a web service developed/maintained by someone else. Before I start this project I want to get an idea of how difficult this will be by doing a test run using an existing web service (developed and maintained by someone else).

I'm looking for recommendations of an existing web service to which I could post an xml document and, if my code is right, get a response that verifies that I'm on the right track.

If there are no other good suggestions then my backup plan is to see if I can add a few local cafes using the Google Places API Web Service.

Thanks in advance