I'm putting this here partially to remind myself of it later and partially to get some feedback for further refinement.
The way I'm envisaging it right now, there are three forces at work in the cosmos: Nature, which simply is (and is thus Neutrality); Law, which seeks to control/subdue Nature to one degree or another; Chaos, which seeks to undermine/destroy Nature.
Neutrality is made up both of creatures who simply go about their daily existence without regard to why and creatures who have chosen, for philosophical reasons, to uphold/protect "the Balance" that Nature represents, said Balance being often impersonal and even amoral.
Law is made up of those who favor Order, whether that order be civilization, hierarchy, or outright domination. There are thus "ethical" distinctions between adherents of Law, some being Good, some being Neutral, and some being Evil. Regardless of such distinctions, all Lawful aligned creatures seek to impose structure on Nature and oppose the entropic character of Chaos.
Chaos is made up of those who revel in destruction, whether it be outright destruction or gradual corruption. Despite different approaches, there are no ethical distinctions between Chaotic beings, since all wish to bring Nature crashing down because they see even its disinterested "order" as too restrictive and stifling. Only destroying Nature will bring ultimate freedom -- the freedom of total annihilation.
So, this gives me the following alignments for my campaign:
I still need to work out how these various alignments relate to one another for the purposes of spells, etc. but I am starting to like this setup a great deal, because it's a nice middle course between the wargam-ish "pick a side" mentality of straight OD&D and the overly schematized to the point of incoherence of AD&D.