Does anyone have any recommendations for either of these validation ASP.Net MVC Validation frameworks?
xVal is pretty much the standard way to do client-side validation in ASP.NET MVC. Actually today Steve Sanderson just released a new version of it :)
The ASP.NET MVC v2 will have client-side validation built in, but it is currently only in Preview 1 so it will be quite some time before that project will be released. You can view more about this on Stephen Walther's blog post...
Microsoft Ajax CDN and the jQuery Validation Library
I would suggest to use xVal until ASP.NET MVC v2 get released.