Perspective! for Comic Book Artists is the resource I've been using in my perspective independent studies. I first read it a few years ago, and I refer to it all the time. I ripped the binding apart and duct taped it back together so I could lay it flat and refer to it while I work. Understanding how to convey perspective in a drawing does not come easy to me - this book has really helped me to get somewhat of a grasp on it. I still have a lot to learn!