Because, hey, how often do you get to talk about this stuff?
Well, not very, for me.
So I've got a Prime Material Plane, yeah, called "The Living World". The usual hoo-hah.
Then I've got two parallel planes: The Realm of Shadow and The Dream Worlds. Shadow is the source of arcane magic (which works in my campaign sorta like it did in Dark Sun -- sucks the life out of everything around it). If you have the right sorcerous ability you can travel through it (there's no teleport in my game but Shadow Walk is greatly beefed up). Shadow is also what powers the undead and is where the soul goes upon death -- actually the soul crosses Shadow to reside in Omean, the Buried Sea. But that's not important right now.
The Dream Worlds are the usual shifty, wobbly place -- home to the fey, the djinn, demons, all the wacky creatures that aren't clearly Shadow-based. The Dream Worlds are the source of psionic power and so psions have a certain affinity with these sorts of creatures. There's also a character class based on being able to negotiate with and control these creatures. The idea is that Dream World denizens can only enter the Living World through a process of binding -- they must be bound in some fashion before they can take a material form. And of course they're always trying to find ways to escape those bonds and keep their form...
And that's it, actually. I don't have any Outer Planes, no Astral or Ethereal Planes. The gods (such as they are) are mostly mortals who have acquired so much power they're no longer really human beings anymore. They make their homes mostly in the Living World, though some manage to create demi-planes of their own within the Dream Worlds.
Hey, I got to talk about it! Lucky me.
So if you like those ideas, JD, help yourself. Sounds like you're working with a more traditional layout, though.