I really like seeing companies build out their own style guide libraries. It's such a huge win in terms of maintaining css and keeping it consistent across an entire site/platform. We went through this process at Trulia about a year ago, and the results had a huge impact[1].

Sadly we never released our style guide to the public, but we did open source the tool for building it: https://github.com/trulia/hologram

It tries to keep things simple by letting you use markdown and html to document your css/js inline and then extracting that into a style guide.

1. http://www.stubbornella.org/content/2013/06/05/creating-livi...