xVal - a validation framework for ASP.NET MVC « Steve Sanderson’s blog
http://blog.codeville.net/2009/01/10/xval-a-validation-framework-for-aspnet-mvc/

I’ve written about validation in ASP.NET MVC more than once already. So have others (Stephen Walther, Emad Ibrahim). It’s an ongoing subject of discussion because the MVC Framework comes with great support for server-side validation (though it isn’t obvious if you come from a WebForms background), but at least as of version 1.0, it won’t ship with any built-in support for client-side validation. I managed to get a few spare days this last week, so I decided to try and formalize lots of these ideas into something solid that you can actually use in real production code - something more than just another throwaway blog post. So here it is: xVal, an open-source project hosted on CodePlex.

your choice of client-side v