I am converting an ASP.NET WebForms website to ASP.NET MVC 3 for a client and by choice we are changing the URL structure as well. Because this may be a common situation, Microsoft introduced a new RedirectPermanent method on Response in ASP.NET 4.0.

If you take a peek at ASP.NET MVC 3, you will see new ActionResult Classes that do the same thing. You are probably familiar with Redirect, RedirectToAction, and RedirectToRoute, but now there are versions of these ActionResult Classes for permanent redirects: RedirectPermanent, RedirectToActionPermanent, and RedirectToRoutePermanent:  

Although out of the scope of this post, for search engine optimization benefits you will want to permanently redirect to the new location of a resource that has permanently moved by issuing an HTTP 301. The previous results only issue an HTTP 302, which means the resource has only temporarily moved.

Hope this helps.