Via Codeplex, and a bit later on Steve Sanderson’s blog I found some information on xVal.
xVal is, as the title of this post states) a validation framework for ASP.Net MVC.

A qoute from Steve's post that got me very exited to start using xVal.

"xVal lets you link up your choice of server-side validation mechanism with your choice of client-side validation library.
It guides you to fit them both into ASP.NET MVC conventions, so everything plays nicely with model binding and errors registered in ModelState."

What this means to me is that I can implement clientside validation via JQuery Validation(http://docs.jquery.com/Plugins/Validation) but if the client does not support JavaScript all validations will also be done serverside.
The validation is also only defined once (on the modal) which makes for much easier maintenance. This is quite a big deal because many of our customers require that the webapplications we build adhere to the accessability rules set by the Dutch government.(http://www.drempelsvrij.nl)

Order a pile of pizza's because I'll be experimenting with xVal and ASP.Net MVC the next couple of days.

PS: if you don't know about DataAnnotaions yet, read this first: http://bradwilson.typepad.com/blog/2009/04/dataannotations-and-aspnet-mvc.html