Using the JSON.NET formatter for normal controllers

Like @rouen suggests, created your own JsonDotNetResult.

This is the one I have in my project:

public class JsonNetResult : ActionResult
{
    public Encoding ContentEncoding { get; set; }
    public string ContentType { get; set; }
    public object Data { get; set; }
    public int StatusCode { get; set; }

    public JsonSerializerSettings SerializerSettings { get; set; }

    public JsonNetResult()
    {
        SerializerSettings = new JsonSerializerSettings
        {
            ContractResolver = new CamelCasePropertyNamesContractResolver()
        };
    }

    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
            throw new ArgumentNullException("context");

        var response = context.HttpContext.Response;

        response.StatusCode = StatusCode;
        response.ContentType = string.IsNullOrEmpty(ContentType) ? "application/json" : ContentType;

        if ((StatusCode >= 400) && (StatusCode <= 599))
            response.TrySkipIisCustomErrors = true;

        if (ContentEncoding != null)
            response.ContentEncoding = ContentEncoding;

        if (Data == null)
            return;

        var formatting = Formatting.None;

#if DEBUG
        formatting = Formatting.Indented;
#endif

        var writer = new JsonTextWriter(response.Output) { Formatting = formatting };

        var serializer = JsonSerializer.Create(SerializerSettings);
        serializer.Serialize(writer, Data);

        writer.Flush();
    }
}

I then have my own baseController that I inherit from to give me JsonDotNet(object viewModel) type methods.

E.g.

protected JsonNetResult JsonNet(object data = null, int statusCode = (int)HttpStatusCode.OK, string contentType = null)
{
    return new JsonNetResult
               {
                   Data = data,
                   StatusCode = statusCode,
                   ContentType = contentType
               };
}

protected JsonNetResult JsonNetForbidden()
{
    return JsonNet(statusCode: (int)HttpStatusCode.Forbidden);
}

protected JsonNetResult JsonNetNotFound()
{
    return JsonNet(statusCode: (int)HttpStatusCode.NotFound);
}

protected JsonNetResult JsonNetNoContent()
{
    return JsonNet(statusCode: (int)HttpStatusCode.NoContent);
}

protected JsonNetResult JsonNetCreated(object data)
{
    return JsonNet(data, (int)HttpStatusCode.Created);
}

protected JsonNetResult JsonNetReload()
{
    return JsonNet(new { reload = true });
}

protected JsonNetResult JsonNetRedirect(string url = null, string contentType = null)
{
    return JsonNet(new { redirectUrl = url }, contentType: contentType);
}

protected JsonNetResult JsonNetClientError(ErrorDictionary errors)
{
    return JsonNet(new { Errors = errors }, (int)HttpStatusCode.BadRequest);
}

protected JsonNetResult JsonNetUnauthorized()
{
    return JsonNet(null, (int)HttpStatusCode.Unauthorized);
}

protected JsonNetResult JsonNetFlashMessage(string message)
{
    return JsonNet(new { flashMessage = message });
}