If you'd like to get started with Ajax, I highly recommend Ajax Construction Kit by Michael Morrison. It's terrific. Morrison's writing is clear, strong, and informative. The sample projects are practical applications that make great starting points for real-world applications. He thoroughly explains the stuff you need to know and doesn't get bogged down in the stuff you don't. Plus he includes just enough humor to keep things light and fun.
The book is broken into three parts: Ajax Boot Camp, Building Real-World Ajax Applications, and Appendices. The first part--Ajax Boot Camp--explains what Ajax is and why it's useful. It also walks the reader through a simple Ajax application, explaining the core concepts clearly.
In the second part--Building Real-World Ajax Applications--Morrison skillfully and patiently guides the reader through ten sample applications, all of which are wonderfully practical. Three of my favorites are: Tapping into RSS News Feeds, Adding an Ajax-Powered Rating System to Your Site (a la Netflix), and A Killer Interface for Image Viewing, which demonstrates how to create a modal image dialogue similar to the popular Lightbox technique.
Within each sample project, Morrison discusses the challenge at hand, the design of his solution, and how he puts it all together and tests it. He then suggests ways to enhance or expand on the sample project and finishes by summarizing any new concepts. Each project is a solid starting point for reader experimentation.
In the third and final part--Appendices--Morrison discusses the past, present, and future of Ajax; provides a "quick and dirty" XMLHttpRequest Reference; and explains the various ways one can use the included live Linux CD.
The companion CD contains all the sample projects and the tools one needs to run and alter them. Microsoft Windows and Mac OS X users can use the sample projects in their own web server environments (if they've set one up), but I'm hoping that they will try booting the live CD instead and experience the joy of Linux as a nice side effect of learning Ajax. Because the CD has XAMPP, Firefox, and the Bluefish editor conveniently bundled and ready to go, booting from the live CD will often be easier than trying to set up a development environment in other operating system environments. A positive experience like this may be just the thing to inspire some new converts to the Linux way.
Morrison created a custom Ajax toolkit for this book rather than using one of the popular frameworks or libraries. It's a rather simple toolkit, which is good because it allows readers of the book to concentrate on learning Ajax techniques rather than the learning curve of a full-blown toolkit.
The combination of the live CD, the great sample projects, and the strength of Morrison's writing make Ajax Construction Kit a clear winner. Anyone new to Ajax would do herself a huge favor by buying this fine book.