I'm going to recommend Douglas Crockford's "JavaScript: The Good Parts". It will really show you how to get the most out of the language and avoid the nasty pitfalls.

As a side note, I attended a talk by him last night on this topic, and wrote up a summary. For a preview of the book, you may be interested in checking out http://www.felixcrux.com/posts/douglas-crockford-talk-waterl...