How to return xml response from controller's action in asp.mvc?

I'm trying to generate rss/feed xml response in an ASP.MVC application. What is the best way to return XML from a controller's action in ASP.NET MVC? There is a nice way to return JSON, but not for XML. I need to do something like

public class FeedController : Controller
    {
        public ActionResult Index()
        {
            return xml("<xmlstring>", "text/xml", System.Text.Encoding.UTF8);
        }
    }