Easy way to install AjaxControlToolKit for Visual Studio 2010

Visual Studio 2010 --> Tools --> Extension Manager --> Install NuGet Package Manager. 

Now you have new menu item "Library Package Manager" inside "Tools" menu for Visual Studio 2010.

Visual Studio 2010--> Tools --> Library Package Manager

PM> Get-Package -Filter AjaxControlToolkit -ListAvailable

PM> Install-Package AjaxControlToolkit 

If you are behind a proxy, most probably you will be prompt for your account to pass it into downloading the package.

"Downloading..." in Visual Studio Status bar

Successfully installed 'AjaxControlToolkit 4.1.60623'.
Successfully added 'AjaxControlToolkit 4.1.60623' to Source.

References:
http://docs.nuget.org/docs/start-here/using-the-package-manager-console