Okay, current planes to be added include:

Skies Plane: a realm of infinite sky, with loose floating mountains hanging inexplicably amidst the clouds.

Towers of Stone Plane: a realm comprised of a dense collection of impossibly high, incredibly steep mountains that are more akin to spears scratching the demon sky. Cities are often carved into the very rock of these spires. 

Spine of Iron: a vast, vertical plane built around a giant chain that has no beginning or end. Huge platforms are built around the central structure that often serve as prisons and slave camps for Slaver Demons

Desolate Labyrinth Plane: A bland, dusky amber plane - it is totally flat and empty, aside from the giant labyrinth of spines snaking it's way across the Plane. To enter is to abandon all hope, and surrender oneself to loss.