Here is a useful collection of AJAX, DHTML, and JavaScript libraries..

• AFLAX
• AjaxAC
• AJAXExtended
• Ajax.NET Professional
• AjaxRequest Library
• AHAH: Asychronous HTML and HTTP
• ATLAS
• Bajax
• Code Snippets
• Cross-Browser.com
• DHTML API, Drag & Drop for Images and Layers
• DHTMLgoodies.com
• DHTML Kitchen
• DOJO Javascript Toolkit
• dp.SyntaxHighlighter
• Dynamic Drive
• DynAPI
• Engine for Web Applications
• FACE
• Google Web Toolkit
• JavaScript Libraries
• JSL - JavaScript Standard Library
• Javascript Toolbox
• jQuery - New Wave Javascript
• JSAN - JavaScript Archive Network
• JSFBGL - Javascript framebuffer graphics library
• Kabuki AJAX Toolkit
• Liberty
• LINB(Lazy INternet and Browser)
• MochiKit
• moo.ajax
• moo.fx
• overLIB
• overlibmws DHTML Popup Library
• Plex Toolkit
• PlotKit - Javascript Chart Plotting
• Prototype
• qForms JavaScript API
• qooxdoo
• Rico
• Ruby on Rails
• Sajax
• Sardalya
• script.aculo.us
• JonDesign’s Smooth SlideShow Library
• Spry Framework for Ajax
• Tabtastic
• Taconite
• Tacos
• The Solvent
• ThyApi
• TwinHelix
• TurboWidgets
• UIZE JavaScript API
• High Performance JavaScript Vector Graphics Library
• WMS Javascript Library
• Yahoo Design Pattern Library
• Yahoo User Interface Library
• Zapatec AJAX Suite
• Zebda
• Zephyr
• ZK