This is something that comes up at least ten times every month or so in the newsgroup comp.lang.javascript. I'll refer you to that FAQ for now.
http://jibbering.com/faq/#FAQ3_1I'll say this about David Flanagan's book though. I've read the 3rd edition and am currently reading the 5th. It is simple enough to understand, but bounces back and forth in my opinion. Also, it doesn't discuss advanced topics at all. Or at least, nothing you couldn't find on a fairly decent resource site.
I would recommend it for an absolute beginner though. I'll say this as well, download the errata and pay attention when something doesn't go right. It's most likely a typo in the book.
If using Internet Explorer, I recommend Microsoft Script Editor.
If using Firefox, I recommend Firebug.
Also, Venkman might be a wise addition to your arsenal.
Depending on your level of expertise and understanding of technical documents you could view the latest revision of the ECMAScript revision or better yet, ISO/IEC 16262, which is basically the updated ECMAScript.
Also, an indispensable resource for JavaScript is the Mozilla Gecko pages at:
http://developer.mozilla.org/I listed the root site so you could see all of the available technologies and areas of interest. Merely click JavaScript if that is your only interest and you're off. Oh, and a JavaScript programmer *must* be aware of the DOM. So I'd suggest delving into the DOM category as well.
Good luck!