Hey,
As of late, I've been noticing that with google, the best docs for a given library/framework/whatever are often not the official documentation. Maybe this is because it takes a user to understand which parts are hard to learn?
Anyway, even with google, the best docs aren't always easy to find (see: the purpose of stackoverflow =D ). so...
What is your favorite unofficial documentation?
Please post each answer separately so we can vote :)