When it comes to digital style guides, a giant PDF alone will no longer cut it. They need to be interactive with explanation and assets. It’s also important to make them a tool for use during the creative and development process not just a deliverable at the end. Defining the guide from the beginning will ensure consistency in the initial development and will provide a path and assistance for continuous development.
The following are some the best examples of interactive style guides on the web today:
1. yelp
The number one example of a digital style guide and asset library.
2. BBC
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Well thought out information architecture and asset archive.
3. HCA
A nice display of web patterns available for builds.
4. Starbucks
This guide just lists and links to a simple example of each component.
5. The Times
This guide is behind a secure login. There are some nice screen captures here that show the functionality.
I would add the Salesforce1 guide to the list as well! The examples section has great stuff.
http://sfdc-styleguide.herokuapp.com/