The ASP.NET AJAX Control Toolkit is a free download and contains more than 40 additional AJAX controls and components that work on top of the core ASP.NET AJAX functionality now built-into .NET 3.5 (and available as a separate download for ASP.NET 2.0).  In addition to having Microsoft developers contribute, the project also has dozens of non-Microsoft contributors adding great features and controls. 

The ASP.NET AJAX Control Toolkit update shipped this week fixes some issues that people were running into when using the control toolkit's extender controls with the VS 2008 Web designer.  The only change made was to adjust the version string number of the control toolkit assemblies (David Anson has more details of the change here).  I'd definitely recommend downloading the update if you are using VS 2008 or Visual Web Developer 2008 Express.

You can also find a steady stream of articles about ASP.NET AJAX and the ASP.NET AJAX Control Toolkit via my Link Listing series (in particular check my post here for a dedicated ASP.NET AJAX link post).  Also read my previous post on using ASP.NET AJAX Control Extenders in VS 2008 to learn more about the integrated design-time support that you now get with the ASP.NET AJAX Control Toolkit in VS 2008 and Visual Web Developer 2008 Express. 

Lastly, check out the great ASP.NET AJAX videos on the www.asp.net site here and here.

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