Barebones — An initial directory setup, style guide and pattern primer by Paul Lloyd

Walmart Web Style Guide

A pattern library of Walmart’s front-end code.

edX Pattern Library · The Visual, UI, and Front End styleguide for edX’s applications

A nicely documented pattern library.

Lightning Design System

A nice combination of style guide and pattern library, with plenty of documentation.

Home · Primer

Github’s pattern library.

As always, it’s great to see how other organisations are tackling modular reusable front-end code (though I can’t imagine why anyone other than Github would ever want to use it in production).

Creating Style Guides · An A List Apart Article

A great article by Susan on getting started with creating a styleguide for any project.

I’ve seen firsthand how style guides save development time, make communication regarding your front end smoother, and keep both code and design consistent throughout the site.