http://blogs.msdn.com/b/ukadc/archive/2012/04/24/asp-net-mvc-amp-jquery-ui-autocomplete.aspx
public static MvcHtmlString AutocompleteFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> expression, string actionName, string controllerName)
{
string autocompleteUrl = UrlHelper.GenerateUrl(null, actionName, controllerName,
null,
html.RouteCollection,
html.ViewContext.RequestContext,
includeImplicitMvcValues: true);
return html.TextBoxFor(expression, new { data_autocomplete_url = autocompleteUrl});
}