[patjoh]

I'm been using http://httpbin.org/ for this.

[izuzak]

Yep. Also:

http://www.mocky.io/, http://ivanzuzak.info/urlecho/, and in some cases: http://hang.nodester.com/

[diminoten]

Oh my goodness, I've been looking for this (mocky) for weeks! Thank you. There really isn't much by way of this particular service, and I found it immensely valuable when I used it last.