Apple Style Guide
The intent of these guidelines is to help maintain a consistent voice in Apple materials. Always an interesting read and reference.
24 ways: Front-end Style Guides
Links to Style Guides
Create a website style guide
BBC - BBC Internet Blog: A new global visual language for the BBC's digital services
BBC's project: the Global Visual Language 2.0, with the aim of unifying the visual and interaction design of bbc.co.uk and the mobile website.