Well, there we are. Three solid documents full of tasty. Planescape has a good bit of material, and Spelljammer even more so. Planescape Conference, if you didn’t see it before, has an appendix of various cosmologies that have appeared in D&D sources, from the major ones to the very obscure. Spelljammer Conference goes even further, listing pretty much every world that’s appeared in a Dungeons & Dragons context. (Neither is complete, of course. I’m way far from having combed every source. But it’s still huge)
And Ravenloft has a thing in it, too.