Question: Does ASP.NET MVC provide a standard validator functionality or do you have to create your own validation manually? If the latter, is there any third party validator available that you can use on ASP.NET MVC web applications?

Answer: 
ASP.NET MVC contains methods like `Html.ValidationSummary()` and `Html.ValidationMessage()`. These are updated automatically if you use `TryUpdateModel`. You could also validate manually and set the errormessages yourself. [Here](http://blog.maartenballiauw.be/post/2008/08/29/Form-validation-with-ASPNET-MVC-preview-5.aspx) is an example of how use it.
David Hayden [wrote an article](http://codebetter.com/blogs/david.hayden/archive/2009/02/03/an-aha-moment-on-mvc-validation-extensibility-in-defaultmodelbinder-bye-to-idataerrorinfo.aspx) over at www.codebetter.com describing a great way to handle validation. Of course xVal is an option but it's always great to have an understanding.