Chris's series (here and here so far) on moral psychology have led me to think through a bit more carefully my view of the philosophical lay of the land when it comes to ethics. Here's my first, rough attempt. Ethically the Great Divide is between Intuitionism and Utilitarianism, and this has been more or less true since the 18th-century; the history of ethics has been, to a very considerable degree, a battle between these two positions. The battle really became heated in the nineteenth century, when the two great representatives were Whewell (Intuitionist) and Mill (Utilitarian). That was a time of giants, when Whewell and Mill between them virtually invented the entire fields of history and philosophy of science as a side issue in the larger ethical war. (The reason is that the Victorians tended to think of moral philosophy on the model of the natural sciences, and therefore it became important for each side to show that their side met the requirements for a progressive scientific discipline and that the other side did not.) It's interesting that cognitive scientists, as portrayed in Chris's posts (and it fits with what I've read elsewhere) tend to be intuitionist in their approach; the the particular divide Chris deals with seems largely to be the traditional divide within intuitionism, between rational intuitionists (like Kant or Whewell) and moral sense intuitionists (like Hume or Darwin). (I say 'largely' because, judging from Chris's comments in the first post, it looks like the ground at this point is as messy in cognitive science as it is in traditional moral philosophy.) I suspect that the influence of Kant would be the reason for it. Intuitionism perhaps also lends itself much more easily to experimental study than other views. It's also perhaps interesting that, overwhelmingly, the dominant approach in ethics today is not intuitionist but utilitarian. I'm not sure the reasons for this. Utilitarianism does lend itself much more easily to the method of semantic analysis + counterexamples, which is popular in analytic philosophy, and I suspect that's the primary reason. I've also found that people in philosophy occasionally have the odd view that utilitarianism is somehow more naturalistic than intuitionism; I'm not sure how widespread this view is, but given how much philosophical work these days is devoted to contributing to the naturalist project, if it is widespread it would also be a likely explanation.
As I said, this is just a rough first attempt, to get the general lay of the land.
(1) Moral Irrealism
1b: Error Theory (Cognitivist Irrealism)
1b1: Intuitionist Error Theory
1b2: Utilitarian Error Theory
(2) Moral Realism
2a: Intuitionism (many different kinds)*
2a1: Rational Intuitionism
2a2: Moral Sense Intuitionism (sometimes simply called 'Intuitionism')
2b: Utilitarianism (many different kinds)
* And I do mean many different kinds. I've put down the two most convenient divisions, but they blur together in many theories (e.g., Conscience Intuitionism like Butler's, or Common Sense Intuitionism like Reid's or Beattie's), depending on how sense-like one's view of 'rational intuition' is.
UPDATE: An anonymous commentator suggests that I'm wrong about utilitarianism being the dominant approach today; and that well may be -- my statement was just based on an impression, and as such could quite easily be wrong. The commentator also suggests that the classification is problematic; but the reasons given are considerably more obscure, and some of them seem based on not taking the Whewell-Mill example seriously, and on not paying attention to the meaning that it sets up for the label 'intuitionism' (in particular, the comment doesn't seem to recognize what intuitionism meant in the time period from which I explicitly took the term). It's just false, for instance, to say that intuitionism in this sense is compatible with utilitarianism, and equally false to suggest that any appeal to intuitions makes one an intuitionist in this sense. For those who need more than I've given above to clarify what I mean by 'intuitionism' and 'utilitarianism', a good place to start is John Stuart Mill's "Whewell on Moral Philosophy"; it's partisan, but it's clear.