I'm using a REST-ful web interface to the server on my current project (having read the excellent book by Richardson and Ruby). For the GET messages, testing via a web browser or wget works well enough. For other message types, and for getting more detailed diagnostics, I found the rest-client from Google Code really useful. I can send any of the standard seven HTTP messages, hack the headers, send different bodies, see all the response headers and set some test predicates on the response. Very nifty ... kudos to the developers.