Does anyone know any good books on the topic of moral realism / moral relativism? The kind of book I would most prefer would be one that would address both (realism and relativism) from a completely objective point of view, discussing the "pros and cons" of both of them. Other sources are welcome too, but mainly I'm looking for a book/books.
One of the more commonly used chapters in ethics classes is James Rachels' chapter on Moral Relativism in The Elements of Moral Philosophy. It's a chapter explaining some of the basic difficulties faced by moral relativism as a palatable moral theory.
For defenses of moral relativism, two of the more famous defenders are David Wong and David Velleman. Wong's book Natural Moralities: A Defense of Pluralistic Relativism (reviewed at NDPR here). I'm no as familiar with Vellerman's arguments.
Returning to who doesn't agree with moral relativism: Plato, Aristotle, Kant, Mill, Locke, ... and most figures in the history of philosophy. A contemporary philosopher who argues against it is Peter Kreeft (see here). Charles Taylor also rejects it at length in his books.
"After Virtue" by Alasdair MacIntyre is a major landmark in contemporary moral philosophy. I don't know if it will answer your specific question but it's one of those works that count as required ready for anybody working in that area.