How about posting the credits page?
I'd love to see who all the writers and artists are.
Also, what web support, if any, may be provided? For example, something this big will probably need "player map" handouts. It would be great if they were available.
Finally, are you going to be offering "World's Largest Dungeon" T-shirts or related stuff? You know, campy things like "I Survived the World's Largest Dungeon" or "All the other d20 modules fit in a small corner of the World's Largest Dungeon," etc...
Marketing, marketing, marketing...