PortalMods.com

Jitsu is a next generation UI toolkit for building rich web applications.
http://www.jitsu.org/jitsu/index.html

Build rich, Ajax-enabled Web applications by using the Eclipse development model.
http://www.eclipse.org/rap/

Open-source, cross-platform, development environment for building Ajax Applications
http://aptana.com/

RichFaces is a rich component library for JavaServer Faces built on Ajax4jsf.
http://livedemo.exadel.com/richfaces-demo/

The Spry framework for Ajax is a JavaScript library for web designers.
http://labs.adobe.com/technologies/spry/

Spket IDE is powerful toolkit(FREE) for JavaScript and XML development.
http://spket.com/

PlatForm introduces you to writing Rich Internet Applications(RIA) using Ajax.
http://www.ajax.org/

The most comprehensive and innovative Open Source multipurpose AJAX frameworks.
http://qooxdoo.org/

OAT is a JS-based toolkit for Rich Internet Application development.
http://oat.openlinksw.com/index.html

An open source framework that makes writing AJAX applications easy.
http://code.google.com/webtoolkit/