My campaign has a slightly different cosmology, based mostly off of Robert Jordan's Wheel of Time.
I have one "real" world, with several secondary worlds, each representing the way the world could have gone if a major crux in time had gone another way. For example, in one world, the elves won the Dream War, and now hold the humans as nothing more than slaves. Individual humans and halflings exist in each world at the same time, while dwarves, elves, and true orcs only exist in one world at a time.
The physical worlds are connected by the world of dreams, taken almost whole cloth from the Wheel of Time. Humans, half-humans, and halflings sometimes touch the world of dreams in their sleep, and whatever happens to them while they're there (wounds, broken bones, etc.) happens to them in the real world. Random thoughts, hidden desires, etc. have a way of coming true in the world of dreams for these mortals that end up there. Some mortals (humans, half-humans, and halflings) learn to control their thoughts while in the world of dreams, and can even learn to enter the dreamworld at will. Any spell effect that references the astral plane, instead refers to the dreamworld IMC. This is also the homeland of elves, dwarves, and true orcs, who can enter the real world through gates and other magic.
Since the Dream War, parts of the dream world "seep" out, and in certain areas enough has entered the real world for the thoughts of sentient races to affect the world in small ways. This is how psionics were discovered, and has led to "gods" forming from the faith of their followers, though these gods are rarely more powerful than powerful fiends or celestials.
Above the world of dreams lies the plane of light, the land of Seraphim (celestials). Good clerics and adepts draw their power from this plane.
Below the world of dreams is the plane of shadow, where fiends cavort, and evil clerics draw their power from.
I don't have an ethereal, or astral plane, nor any of the elemental planes.