Since you seem to be a planes junkie, I recommend Beyond Countless Doorways from Malhavoc Press. Some of the people that worked on Planescape also worked on this book, and it provides an interesting alternative to the standard Great Wheel cosmology. Though if you are looking for more Great Wheel stuff, this book isn’t so useful. I myself am a big fan of orrery-style cosmologies, a la Eberron.
– Adrian 2007-11-08 18:51 UTC
Hm, after reading some reviews  this seems to be just my kind of book. In fact, I ordered it from Amazon Marketplace just now. Thanks for the recommendation. I’m flexible when it comes to cosmology. The important part is that angels and demons, the heavens and hell are all places to travel to.
– AlexSchroeder 2007-11-08 20:05 UTC