Is there any ajax toolkit for asp.net MVC
As MVC does not have ViewState or the Web Forms postback model the AjaxControlToolkit will not work with it.
There is a project to do this (http://mvccontroltoolkit.codeplex.com/) but it's not yet released.
There are numerous blogs where have got different controls working but to be honest I'd suggest looking at jQuery and its plugins (http://www.jqueryui.com/). MVC lends itself far more naturally to these, it is not control-based.
Here's another resource talking about this: http://www.hanselman.com/blog/ASPNETMVCPreview4UsingAjaxAndAjaxForm.aspx
In addition, ASP.NET MVC lends itself quite easily to making your own amazing ajax controls, especially when combined with jQuery.
The emphasis in ASP.NET MVC is more on HTML and client-side code when talking about user-control similar to those in the AJAX Toolkit - you may like to check out the excellent http://www.jqueryui.com/ for some good client-side controls.