Here's a simplified (and working) version of akousmata's localized enum extension:
public static string DisplayName(this Enum enumValue)
{
    var enumType = enumValue.GetType();
    var memberInfo = enumType.GetMember(enumValue.ToString()).First();
    if (memberInfo == null || !memberInfo.CustomAttributes.Any()) return enumValue.ToString();
    var displayAttribute = memberInfo.GetCustomAttribute<DisplayAttribute>();
    if (displayAttribute == null) return enumValue.ToString();
    if (displayAttribute.ResourceType != null && displayAttribute.Name != null)
    {
        var manager = new ResourceManager(displayAttribute.ResourceType);
        return manager.GetString(displayAttribute.Name);
    }
    return displayAttribute.Name ?? enumValue.ToString();
}
Note: I move enumType from a parameter to a local variable.  
Example usage:
public enum IndexGroupBy 
{
    [Display(Name = "By Alpha")]
    ByAlpha,
    [Display(Name = "By Type")]
    ByType
}
And
@IndexGroupBy.ByAlpha.DisplayName()
Here is a editor template that can be used with the extension method above:
@model Enum
@{    
    var listItems = Enum.GetValues(Model.GetType()).OfType<Enum>().Select(e =>
        new SelectListItem
        {
            Text = e.DisplayName(),
            Value = e.ToString(),
            Selected = e.Equals(Model)
        });
    var prefix = ViewData.TemplateInfo.HtmlFieldPrefix;
    var index = 0;
    ViewData.TemplateInfo.HtmlFieldPrefix = string.Empty;
    foreach (var li in listItems)
    {
        var fieldName = string.Format(CultureInfo.InvariantCulture, "{0}_{1}", prefix, index++);
        <div class="editor-radio">
            @Html.RadioButton(prefix, li.Value, li.Selected, new {@id = fieldName})
            @Html.Label(fieldName, li.Text)
        </div>
    }
    ViewData.TemplateInfo.HtmlFieldPrefix = prefix;
}
And here is an example usage:
@Html.EditorFor(m => m.YourEnumMember, "Enum_RadioButtonList")