Here you'll find the basic layout of the planes, links to descriptions of the individual planes, rules for the planes, and just about anything else I have or come up with for planar information.
The Planes at a Glance
The Plane of Time - At the center of the multiverse, not many people know about this plane, but without it, nothing would work. From here, the immutable flow of Time trickles forth through the planes, dribbling lazily across the cosmos to fill all of creation with the steady ticking of the clock. An interesting place of note in this plane is the Citadel of Eternity, and the Throne of Dominion within it.
The Ghost Plane - The transitive plane linking the Plane of Time to the Elemental Planes, this plane is a dangerous place to visit - one wrong step, and you can easily find yourself wandering forever among frozen posibilities of past, present, and future. All of the multiverse is echoed in frozen timescapes here - from the distant origins, so far back that even an elf would die of old age before reaching the first moment, to all the possible versions of the past, present, and unimaginably distant future.
The Elemental Planes - The basic forces of creation, and the forms taken by the merging of those elemental forces. Like a cosmic eggshell, they surround and protect the Plane of Time from those who would try to enter and seize the Throne of Dominion's power. More than this, however, they are the fundamental building blocks of the mortal planes - raw genesis given form and power. The gods who rule here are no mortal gods - they are the elemental force of their plane given awareness and control.
The Ethereal Plane - Linking the Elemental planes with the Primes, the Ethereal is a dangerous place, constantly filled with tides of raw elemental energy. The unwary may find themselves suddenly slammed into by a torrential wave of elemental power, ripping and shredding at their body - but sometimes, these elemental forces imbue those they touch, granting peculiar strengths and weaknesses to the victim.
The Plane of Shadow - Like a thick tar, the Plane of Shadow connects all of the Primes together, like a pool with delicate crystal balls floating in it. Mirroring the Prime nearest the area, Shadow is a place of subtle dangers to the planar traveller - full of soft shadows, quiet sounds, and hidden dangers. Those who dwell too long upon this plane risk becoming a creature of it, forever bound to the dark places of the world.
The Prime Material Planes - The lands of mortals - each plane a distinct and finite size, hundreds of billions of miles across, bounded by the delicate crystalline edge of the plane as it floats in Shadow. And yet, despite the finite space, the number of Primes seem infinite - alternate versions of identical worlds, worlds so alien as to be unknowable, all are contained within the Prime planes. These are also the last planes formed of the stuff of elemental energies - farther out, the planes become more rarified and unusual in nature.
The Astral Plane - A plane of the mind, the Astral links the Prime planes with the Outer Planes, funnelling the dead, the belief and worship of mortals, and conducting those mortals who dare to venture out to the Outer Planes on their way. The hazards of the Astral come in two flavors - the mind-eroding astral mists, and the terrifying trembling of the plane known as the Psychic Wind - the result of lost mortal minds and souls, flowing through the plane like a bizarre alien water.
The Outer Planes - Unlike the Outer Planes of the standard AD&D 2E cosmology, these planes are not planes of alignment - rather, they're planes of ideas, ideals, beliefs, and dreams. The prison-plane of Hades, the paradise of Celestis, the twin planes of Ohtori and Ceirrus, hom to the Rose War... All of these and more exist out past the Astral, home to gods, angels, and demons, as well as the souls of the dead. Out here are wonders and mysteries beyond the grasp of mortal minds - sometimes the very rules of reality vary from plane to plane, or even from layer to layer.
The Plane of Mirrors - On the very out edge of the multiverse - if infinity can be said to have an edge - is a peculiar plane, filled with a seemingly infinite number of crystalline shards, each one showing a single plane in the facets as it floats in the void. Among the few who know of this plane, many theories are tossed around as to what the purpose of the plane's existence is, but none know the true purpoe of the plane's existence.
The Demiplanes - The Demiplanes are pocket dimensions, scattered around the cosmos. Some branch off of the Astral, some the Ethereal; a few grow from the Plane of Shadow, and on those planes where the god Akio has followers, tiny crystalline bubbles cling to the plane's edge, home to his priests and servants. The demiplanes are places of infinite possibility, each one bent to the whims of the one who created it.