Ajax

Ajax is a free framework for quickly creating a new generation of more efficient, more interactive and highly-personalized Web experiences that work across all the most popular browsers.
http://ajax.asp.net/

This website gives video tutorials for Ajax Programming .

Beta 2 features the following improvements over the October Beta release, including:

UpdateProgress control. The UpdateProgress control is now part of the supported core.
Client-side localization. Client scripts can now automatically retrieve localized resources from the server, making it possible to create locale- and region-aware Web interfaces.
Simplified event binding API. Added functionality for binding and detaching multiple event handlers to a DOM element with a simple function call, which reduces the amount of script and helps prevent memory leaks.
Client control CSS-based style support. Added functionality for using script to add, remove, and toggle CSS class associations on client controls.
Performance and stability improvements
Control designers are now installed in a separate assembly for less server overhead at runtime.
The ScriptManager control has support for configuring a timeout and for detecting scripts that time out when loading.
Script components can now register for dispose semantics with the ScriptManager control to avoid memory leaks
Debugging and tracing improvements. Better support for identifying and diagnosing issues during development and deployment.