I'd like to see some D&D books based on the Wizard of Oz book series (not the movie, the original books by Baum!), a D&D version of Final Fantasy, and maybe some other settings like Earthsea... NEW stuff in other words, not just the same old type of worlds like Greyhawk and Forgotten Realms (not that I dislike those, but I'd like to see something completely different!) The Wizard of Oz series has characters that would fit right in with Planescape; a Tin Man, Scarecrow, Talking Lion, etc... WIERD stuff! and the characters in his later books are even odder, if that's possible...
Campaign settings you'd like to see?
Some themes are similar (and some are really, really brilliant on their own), but just cutting-and-pasting Oz into Planescape wouldn't be a good idea.
Definitely plunge into its soft, squishy membrane to ravage it for idea-fodder, though.
It's already happened. Aren't there swarms of sopoforic-spewing red flowers somewhere?
I think you could get quite a bit of milage out of Oz, which (in the books) does a nice job of being bizzaro wierd and childish at first glance, but with deeper layers of meaning and internal logic (at least as far as I remember from University days...)
AnimeFan, I recommend checking out Dungeonland and Beyond the Magic Mirror (both by Gary Gygax), which are basically Alice in Wonderland and Alice Through The Looking Glass translated into AD&D - they're primitive by today's standards but with a Planescape makeover I think they'd be great.
Um, no offence man, but Planescape isn't just about being weird. It's about the power of belief, the vastness of infinity, and the wonderful tapestry of story that's been hung out for us to play around with, live in, and change by our actions, for better or worse.
The Wizard of Oz books were a good read, but beyond stealing a few ideas as seeds of something else, I don't think they really fit PS all that well. Maybe it's just me, though. Your mileage may vary