I'll add the poll to the site tomorrow, which gives you 1 more day to add your suggestions to my first monthly audience participation event!
I have just finished reading The Phantom of the Opera, and I must say that it reads like play report from an adventure module.
It wouldn't be all that difficult to turn the Phantom and his dungeon into a D&D adventure. 5 cellars, an underground lake, a horrible villain with some pretty clear motivations, and that fantastic rat catcher... It's more immediately translatable into adventure terms than either the first Oz book, or Alice in Wonderland, even though both of those offer a richer and more unique setting.