Hello!
I admit you best me in FR lore here. The neutral lower planes??? What would that be? I thought they pretty much had it covered between the Abyss and the Nine Hells. Though I think it somewhat more interesting to have a half-demon in the devils' realm than in a neutral plane.
Well I don't really know *that* much about it, but two examples would include Gehenna (Also known as the Grey Waste) and then Canceri, which is slightly more on the chaotic side but still Neutral Evil in essence.
Gehenna - Populated mainly by the Yugoloths, one of the more fearsome creatures of the lower planes. Unlike Canceri, four volcanoes in stages of dormancy floating in an infinite void, each of them somehow alive and tempting travellers. To get your soul by any means possible - or some other such.

In addition - Gehenna is also a no-place that drains color from your body and spirit, stealing everything possible, and it's also the site of the worst or most twisted battlegrounds in the Blood War.
Canceri - Poisonous jungles, acid swamps, destructive waters, strung like a string of rotten pearls nestled within one another. Essentially a prison plane - home to the gehreleths, one of the more dangerous types of demons. Canceri is also called the Red Prison - because it is as strong with it's strength sapping as the strength of those imprisoned. Being there, is a poison apparntly, you get weaker as you go, similar to the effects of the Grey Waste (Gehenna).
That's all I really know, and much of that was gathered by Planescape Torment, but a few other sources may help too.
http://en.wikipedia....iki/Outer_Plane Outer planes information thanks to Wikipedia
http://en.wikipedia.org/wiki/Yugoloths Information on the predominants of the Grey Waste
Hope some of this is of use.

I very much look foward to see where this story will head next.
Edit: Typos, must hurt typos!
Edited by Solar's Harper, 10 January 2008 - 07:58 AM.