There was a purchase of the rights to the early Xanth novels almost a decade ago, but the option expired. At the time, SFX weren't necessarily up for the challenge and LOTR hadnt proven that such a movie could be a commercial success. Any of the Xanth novels would be big hits in my opinion and the would definitely make my list! (In fact, Dragon on a pedestal, did make my list of most personally influential books in a hub written a few years back)
Great Choice, keep em coming!