Mockable - Quickly define some REST or SOAP endpoints and have them return json/xml (dummy) data.
Postman - The Collaboration Platform for API Development
RequestBin - RequestBin.com gives you a URL that collects requests you send to it so you can inspect them in a...
MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.
WireMock Cloud - Fast and simple API mocking in the cloud, powered by WireMock.
WireMock - WireMock - a web service test double for all occasions.