Demo web service clients for Moodle 2
They work for any Moodle 2.X excepted when mentioned (for example REST-JSON will only be available in Moodle 2.2 and later)

Note: it is sometimes not easy to know how to format the parameters (they can be found into Admin block > plugins > Web services > API documentation).
In order to help, Patrick Pollet wrote a script in PHP at http://tracker.moodle.org/browse/CONTRIB-3472. It produces all the 'skeleton' parameters.