Planar Sourcebooks?

[Taperat]

Hopefully this is the right place to put this. My favorite 3rd party product of all time is Malhavoc Press's Beyond Countless Doorways, a planar sourcebook originally written for D&D 3.5. I love its approach to planes, where each is a distinct (and sometimes very weird) world and not some grand 'archetypal concept', like the plane of fire or the abyss. My question is, does anybody know of any other books of this sort, or any online resources where people have done similar things? The system it's written for doesn't matter to me, I'm just interested in more planar ideas to spark my creativity.

[Jeven]

I haven't read it yet, but Dark Roads & Golden Hells by Kobold Press is supposed to be very good. Its written for Pathfinder as well.
http://paizo.com/products/btpy8tm3/discuss?Dark-Roads-Golden-Hells

Of Paizo's books the Book of the Damned series is excellent. The one on Hell is my favorite.
http://paizo.com/products/btpy8a6f?Pathfinder-Chronicles-Book-of-the-Damned -Volume-1-Princes-of-Darkness

[Knoq Nixoy]

Dark Roads and Golden Hells for me is even better than Beyond Countless Doorways

of Paizo's planar books I agree that Princes of Darkness is the best, even though I prefer other planes

other interesting books:

The Plane Below: Secrets of the Elemental Chaos (4e)
Classic Play: Book of the Planes (Mongoose)
Seven Civilizations (Penumbra)
Faeries (Bastion Press)
Gary Gygax's Cosmos Builder
Chessboards: The Planes of Possibility (The Primal Order)

online resources:

mimir.net
planewalker.com or mimir.planewalker.com

[Brother Fen]

Todd Stewart wrote the book for PFRPG - The Great Beyond. It's packed with fascinating details on the nature of the cosmos.

[Jeven]

The Great Beyond gives a good overview, but because all the planes are crammed into just 60 pages it offers only a very brief glimpse of each one.

Princes of Darkness is better because it provided rich and vivid descriptions of each of the nine layers of Hell. After reading it you feel like you know Hell.

The Lords of Chaos focuses on the many Demon Lords rather than the realms of the Abyss.

Horsemen of the Apocalypse lies somewhere between the two. Abaddon is less varied than the other planes and the descriptions are less vivid and memorable than the Hell book.

Like Knoq Nixoy, Hell was the one I was least interested in, but I enjoyed that book the most because it has very rich descriptions which make the place easy and enjoyable to visualize.