Eloquent Javascript now in print
nostarch.com
nostarch.com
http://dmitrysoshnikov.com/ecmascript/javascript-the-core/
These series of articles are probably the deepest series into the language on the Internet (surpassing even Crocford's articles as far as depth goes).
The pace is perfect, and even people who are already familiar with JavaScript can get something out of it.
Just bought myself a copy.
http://eloquentjavascript.net/
My opinion:
It is a book that anyone of any skill level can get something out of. It is one of the few books that is technically a beginners book, but it does not talk to you like you are stupid.
Most importantly, it is focused just as much on software craftsmanship as it is teaching you javascript. It is a great introduction to functional programming and the 'good parts' of object oriented programming.
Why should you buy the book if it is online for free? Well, I have extreme respect for people who try to teach others and give away their work for free. I like to support them in any way possible.
Crockford's book is great, but I don't really subscribe to the 'if I could only buy one book on x' mentality. I prefer to get my information from as many sources as possible and Haverbeke should definitely be one of of those sources.
Well, if it is a good read, I eagerly will shell out money for a printed copy that I do not have to read off a screen. In a way, it's incentivizing, wishing to reward such an act of open collaboration.
Also, I believe if online feedback is used properly, definitely will result in a superior book product.
Or just read through his site: http://javascript.crockford.com/
I only wish his linter were better. I haven't poked at the recent update (!) very much, but it was almost un-usably incorrect for quite a while, and removes one of my favorite tools for making javascript look nicer: functions as objects (ie, with properties). Instead, he preaches a super-watered-down version where functions are mere constructors for objects, and nothing else.
Another outstanding beginners reference: DOM Scripting by Jeremy Keith. Clearly explained and encourages good habits.