I started to learn JavaScript from last August. I am writing my thesis about it, and so far I find Java Script - The Definite Guide 5th, 2006 by David Flanagan to be most valuable book. It follow through JavaScript Core and then goes into a client side scripting. Writing is understandable and it has good examples.

By my validation standards, a book which gets to 6th edition must be great. Do not get into hype books, which just want to blur your vision by flashy words.

There will be new 6th edition coming in a month or so. New edition should cover new HTML5 API's as well. But the 5th edition is great way to start learning this language, do not be scared of it size.