Ajax has been around for yonks now and it’s not news. However, many people seem to still shy away from learning JavaScript. Having JavaScript or more specifically ECMAScript under your belt is really beneficial. JavaScript is used in many areas other than the browser; ActionScript, FireFox’s Plugins, Server side (i.e. Aptana Jaxer), Google's V8 and various others. To mention a quick extra note on V8 as its fairly new news, its the JavaScript engine behind Google Chrome however its standalone and can be used in any project you wish. Find out more about it at the V8 webpage. It’s a good way to get into dynamic programming if you are more used to languages such as C# and Java. This is a list of the things I think you should check out if you want to learn JavaScript. Free stuff;

• Yahoo UI Theater – Various videos about JS. "The JavaScript Programming Language" and "Advanced JavaScript" by Douglas Crockford are particularly good
• Ajaxian – Free website about Ajax news but its surprising how much you can learn by reading what people are creating.
• Douglas Crockford’s world wide web – Various articles on JavaScript by the same guy as the good YUI videos
• Browser vendor docs; Mozilla, Safari, Opera, V8 (I hate the MS internet explorer docs!)

Books;

• JavaScript: The Definitive Guide by David Flanagan; This is a really meaty book (1018 pages) but its full of great information. Personally I prefer a book that’s more concise and to the point but its still very good.
• JavaScript: The Good Parts by Douglas Crockford; Quite a short book but full of interesting information. If you like Douglas Crockfords style in the video’s or on his website it’s well worth checking out.

The ugly (things I would avoid);

• Professional JavaScript for Web Developers by Nicholas C. Zakas; I found this quite out dated and had numerous errors or encouraged methods that are generally accepted to be bad.
• Most other JavaScript books. I've not read many others but I've heard grave warnings about many of the books that are a little bit older. Make sure you check out reviews before you buy!

If you have any more resources that you think are worth adding let me know if the comments!