PHP REST Client
http://github.com/tonychang/PhpRestClient old version uses identity/key pair.
https://github.com/keithsct/PhpRestClient this version uses p12 files for x.509 certs.
https://github.com/UWEnrollmentManagement/Person this version contains a framework for polling the restful resources.
C#.Net REST Client
CSharp Client Sample Code
Ruby on Rails REST Client
Ruby on Rails Client Sample Code
Ruby Gem
https://github.com/UWFosterIT/uwsws
JavaScript Node.js
https://github.com/UWFosterIT/node-uwsws
Python REST Sample Code
https://wiki.cac.washington.edu/display/infra/Python+Code+Snippets+for+UW+Groups+Web+Service