The setup I'm using for my game system's default setting is what I call the Heliocentric Planar Model. At its heart is The Source, a place of infinite potential from which all matter, energy and spirit in the cosmos originates. It's spiritual presence is visible in the Mortal World as the Sun (hence the name of the model). As this infinite potential flows from the Source, it "cools" into discrete elements (air, earth, fire, water) and then into combinations of elements (cold, storm, metal, plant) and finally at the distance of the Mortal World they are able to combine into life (air/breath, earth/body, water/blood, fire/body heat).

Primal Spirits representing each of the elements warred over the Mortal World. The losers (who came to be called demons) were cast into the Outer Darkness and a Great Barrier errected to hold them outside of Creation. But the war shattered the Mortal World's spiritual reflection so that instead of perfectly reflecting it's light, it instead scattered it across the Barrier like motes off a mirror ball... giving birth to the stars, each a reflection of some aspect of the Mortal World.

Eventually this spiritual power gained self-awareness and became the Astral Gods, whose power comes from the degree to which the Mortal World reflects its aspect (which is why the god of slaughter can get away with having virtually all of it followers wiped out... it gains power from the slaughter itself; believer or unbeliever; not the number of worshippers it has). Normally souls would flow back to The Source in death (whether they're reincarnated, broken up for raw material or enter some paradise is one of the great unknowns of the cosmos), but devout worshippers can earn a place in one of the Astral God's courts if they want a more assured afterlife (thiugh possibly less glorious if the people who say The Source is a paradise are right).

The other alternative for souls who fear The Source and will not submit to the Astral gods is to hide in the shadow of the Mortal World where the light of The Source cannot reach. These lost souls native to the Shadow World are the undead; who sustain themselves on the life of the living since the direct light of The Source/Sun would burn them to ash.

That's the gist of it anyway.

In my DCC campaign there's a set of planes based VERY loosely on the Qabalistic Tree of Life. Of course, the campaign being what it is, a lot of it is a very gonzo interpretation of the same.