It might be a good idea to sticky a thread detailing the sources a contributor to this project is expected to be familiar with. I own the 2e Planes of Conflict boxed set, which covers the Gray Waste from a player's and a GM's points of view, and I own the 2e Monstrous Manuals 1-3. Like anyone else, I have access to the 3.5 SRD. However, a good deal more is apparently known, and probably being assumed for contributors. If the overseer(s) of the project would kindly list a "core curriculum" that a contributor should be familiar with, I would appreciate it (and possibly buy sources requested that I don't own).
What's a contributor expected to know?
Actually, there isn't anything you really need to contribute. As I've written somewhere before, the project is meant to give contrasting views, even contradictory ones.
Things were done like that in "Faces of Evil", and it was one of the main reasons why that book was so great: It gave the power back to the DM, because the DM doesn't have to follow the letters of the book. Instead, everythng was "possible", a theory or a perspective, but you could never be perfectly sure about what you read. From my point of view, this fits perfectly to Of Darkest Gray.
Put short, if you want to follow some existing idea, you should of course know the sources where that idea comes from (for example, if you wanna write about the Night Hag in Torment, you should've played the game recently). But otherwise, as long as you have good explanations for everything, you don't need to base your ideas on any specific book.
What he said!
I guess it's worth noticing, that night hags were obviously inspired by character from Eastern-European folklore and Slavic mythology. There's a tale about "Yaga Hag" (in Torment, night hag Ravel is even called Yaga Sister), a hag that lives deep in the forest, in a hut. She lures there children lost in woods, then roast and eat them.
Or to give her full name, Baba Yaga although Primer hags are based as much on British and Breton folklore's wicked old ladies, and the nordic "Angel of Death." Wikipedia (where the above link goes) is a quick jumping off point for research. Baba Yaga has actually featured in various D&D adventurers and suppliments over the years.
As regards the core knowledge suggestion - there are actually quite a few folk on Planewalker.com who never ran 2nd ed (myself included, although I've played it a lot) so I'd rather a "recommended reading list" rather than required knowledged. But hey, its good to get people thinking professinally about a project from the start. A list of recommended reading would be helpful to everyone (and not just D&D materials)
I'll put all those things up in the next couple days. I've got some free time from the weekend on, then I'll write up everything that's needed to get this thing rolling!
I'm not sure all of what joyblood would recommend, but our Encyclopedia here isn't actually that bad a location to start either.
If you have a subject in mind - each of the entries is (or Should be!) complete with cite references. So that way if you've got something you're working on - you can find out where to find out more about it.