Head First AJAX free Download

Ajax is a way of  designing and building web pages that are as interactive and responsive as desktop applications. So what does that mean for you? You handle things at the client’s browser whenever you can. Your pages make 
asynchronous requests that allow the user to keep working instead of  waiting for a response. You only update the things on your pages that actually change. And best of  all, an Ajax page is built using standard Internet technologies, things you probably already know how to use, like:
XHTML, CSS, JAVA Script

This Book is Really Very helpful for those who want to learn Ajax.