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.
In addition to Douglas Crockford's book, which is excellent, I'd also recommend the 2nd edition of "Professional Javascript for Web Developers" by Nicholas Zakas.
the crockford book is really good, but in reality the best thing is practice. javascript is a tricky language, and crockford helps to simplify it, but you can get a lot of practical knowledge on how to use the language and jquery just by practicing a lot (sorry). but read crockford too :P
also heard an oreilly cookbook for js is coming out soon, may be worth looking into if youre into those.
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...