SUN Developers
Put the power of Ajax in your web and portal applications with these Sun-supported and open source tools and technologies.
http://developers.sun.com/scripting/ajax/index.jsp

Ajax Matters
AJAXmatters.com was launched in 2004 as a blog on the then nascent AJAX technology.
From July 2007 we redesigned the site and redirected the focus to creating a detailed knowledge base for AJAX developers. Instead of short blog entries the site provides indepth articles for the novice and experienced AJAX developer alike.
http://www.ajaxmatters.com/

Mini Ajax
MiniAjax.com / A showroom of nice looking simple downloadable DHTML and AJAX scripts
http://miniajax.com/

Qooxdoo
qooxdoo is a comprehensive and innovative Ajax application framework. Leveraging object-oriented JavaScript allows developers to build impressive cross-browser applications. No HTML, CSS nor DOM knowledge is needed.
http://qooxdoo.org/

Ajax Impact
AjaxImpact.com is an informational portal for Ajax developers, Its the one stop resource for Ajax Tutorials, frameworks, tools, libraries, articles, books and news.
http://www.ajaximpact.com/tutorials.php

W3 Schools
AJAX stands for Asynchronous JavaScript And XML. AJAX is a type of programming made popular in 2005 by Google (with Google Suggest). AJAX is not a new programming language, but a new way to use existing standards. With AJAX you can create better, faster, and more user-friendly web applications. AJAX is based on JavaScript and HTTP requests.
http://www.w3schools.com/ajax/default.asp

Alista Part
The start of 2005 saw the rise of a relatively new technology, dubbed “Ajax” by Jesse James Garrett of Adaptive Path. Ajax stands for Asynchronous JavaScript and XML. In a nutshell, it is the use of the nonstandard XMLHttpRequest() object to communicate with server-side scripts. It can send as well as receive information in a variety of formats, including XML, HTML, and even text files. Ajax’s most appealing characteristic, however, is its “asynchronous” nature, which means it can do all of this without having to refresh the page. This allows you to update portions of a page based upon user events and provides one of the cornerstones of Rich Internet Applications (RIA) referred to in discussions of “Web 2.0.”
http://www.alistapart.com/articles/gettingstartedwithajax

Adaptive Path
Ajax: A New Approach to Web Applications
http://www.adaptivepath.com/ideas/essays/archives/000385.php

Ajax php Magazine
http://ajax.phpmagazine.net/