Community

I recommend:

Planescape -> Given the success of Tony DiTerlizzi in the children's book world, and the available artwork lying around, seems like an easy win. You can make the game based around portal keys and Sigil.

Birthright -> Kingdoms, dead gods, cool stuff. The players are heirs to the gods.

Spelljammer -> Wizards on space ships? What's not to love?

edit: okay, there's bias in the first one but I think my argument's sound. ;-)

eta2: Another relatively cheap thing to do is make browser based mini games for the settings. Y'all need to get people to give a frack about D&D again, seems like a good way to do it. If people love the world they'll at least buy the CRPGs when they come out.