Finally the wait is over and ASP.NET AJAX final version is out. You can download it here.

ASP.NET AJAX 1.0

ASP.NET AJAX 1.0 delivers a rich client-side AJAX library that provides cross platform, cross browser support for a core JavaScript type-system, JSON-based network serialization stack, JavaScript component/control model, as well as common client JavaScript helper classes.  ASP.NET AJAX also delivers a rich server-side library that integrates AJAX functionality within ASP.NET, and enables developers to easily AJAX-enable existing ASP.NET 2.0 sites with minimal effort.

ASP.NET AJAX is available for free, and can be used with ASP.NET 2.0 and VS 2005.  It is a fully supported Microsoft product, and is backed by a standard 10 year Microsoft support license (with Microsoft Product Support available via phone 24 hours a day x 7 days a week).

ASP.NET AJAX Control Toolkit

In addition to the fully-supported ASP.NET AJAX 1.0 release, you can use the more than 30 free ASP.NET AJAX enabled controls available within the ASP.NET AJAX Control Toolkit.  The control toolkit is a shared-source collaborative project built together by a team containing both Microsoft and non-Microsoft developers (visit the CodePlex Project to learn more, or volunteer to contribute).  All source for the controls is provided completely for free (with full re-use and modification rights).

The majority of controls within the ASP.NET AJAX Control Toolkit leverage the "Control Extender" pattern that the core ASP.NET AJAX library introduces, and which delivers a super powerful way to easily enable specific AJAX scenarios on a site with minimal effort.

Check ScottGu's Blog for more details...