If you are thinking about the client side of things, I would suggest checking out Matt Sukowski's PEST.
You will find the repository on GitHub:
https://github.com/educoder/pest
Also check out this thread:
PHP REST Clients
Update 2013/12/13:
This is very much a live open source project, Matt Sukowsky handed it over to new caretakers this summer because he didnt feel he could spare enough time, and there has been lots and lots of commits since then. So Pest is better than ever for doing Rest in PHP :)
