Routing for .json and .xml
Details(id)
{
    $data = $this->MyController->findById(id);

    if($this->requestType == "json")
    {
        respondAs("json");
    }
    else if($this->requestType == "xml")
    {
        respondAs("xml");
    }
    else
    {
        //does default - html view
    }

    $this->setViewVariable("data", $data);
}

routes.MapRoute(
    "Default",
    "{controller}/{action}/{id}/{type}",
    new { controller = "Home", action = "Index", id = UrlParameter.Optional, type = UrlParameter.Optional });

public ActionResult Index(int id, string type)
{
   if(type == "json")
      return View("JsonView");

   //etc
}