Recommended reading (a small excerpt from the intro)

The following books (in no particular order) all have high recommendations from editors and the developer community alike, and any of them should serve as very good lead-ins to the chapters that follow.

• Ajax in Action, by Dave Crane, ISBN 1932394613

  "Web users are getting tired of the traditional web experience. They get frustrated losing their scroll position; they get annoyed waiting for refresh; they struggle to reorient themselves on every new page. And the list goes on. With asynchronous JavaScript and XML, known as "Ajax," you can give them a better experience. Once users have experienced an Ajax interface, they hate to go back. Ajax is new way of thinking that can result in a flowing and intuitive interaction with the user.

  "Ajax in Action helps you implement that thinking--it explains how to distribute the application between the client and the server (hint: use a "nested MVC" design) while retaining the integrity of the system. You will learn how to ensure your app is flexible and maintainable, and how good, structured design can help avoid problems like browser incompatibilities. Along the way it helps you unlearn many old coding habits. Above all, it opens your mind to the many advantages gained by placing much of the processing in the browser. If you are a web developer who has prior experience with web technologies, this book is for you."

• Professional Ajax, by Nicholas C. Zakas, ISBN 0471777781

  "Professional Ajax discusses the range of request brokers (including the hidden frame technique, iframes, and XMLHttp) and explains when one should be used over another. You will also learn different Ajax techniques and patterns for executing client-server communication on your web site and in web applications. By the end of the book, you will have gained the practical knowledge necessary to implement your own Ajax solutions. In addition to a full chapter case study showing how to combine the book's Ajax techniques into an AjaxMail application, Professional Ajax uses many other examples to build hands-on Ajax experience."

• Ajax Patterns and Best Practices, by Christian Gross, ISBN 1590596161

  "Ajax Patterns and Best Practices explores dynamic web applications that combine Ajax and REST as a single solution. A major advantage of REST is that like Ajax, it can be used with today's existing technologies.

  "This is an ideal book whether or not you have already created an Ajax application. Because the book outlines various patterns and best practices, you can quickly check and verify that you're building an efficient Ajax application."

• Understanding AJAX, by Joshua Eichorn, ISBN 0132216353

  "Building on what you already know, this fast-paced guide will show you exactly how to create tomorrow's richest, most usable Internet applications. Joshua Eichorn teaches through sophisticated code examples, including extensive back-end sample code based on PHP, the world's #1 server-side language.

  "You won't just learn how to code AJAX applications: Eichorn covers the entire development lifecycle, from use cases and design through debugging. He also presents detailed application case studies, including a start-to-finish update of a non-AJAX application that addresses everything from feature improvements to changing usage patterns."

The following websites also have a wealth of information available, most of which should prove useful enough to bookmark for easy access.

• W3C
• mozilla developer center
• Quirks Mode
• css discuss

I'll also post an edited version of my bookmarks, since I use the references constantly for my day-to-day work, let alone when I need to look something up for the book. I just wanted to post the "I visit at least one of these sites almost every time I look up anything related to an Ajax problem" links. When I see others post a list of most-used references of theirs, I generally find at least one I didn't know about or look into enough to realize its full value.