We've had Frankenstein and Wizard of Oz previously suggested, haven't done them though. Also in the vein *ahem* of Frankenstein, Dracula might be interesting, as I mentioned last month.
Something more modern might be fun too, like one of the newer fantasy authors that perhaps not everyone has read.
But I'd also be interested in more suggestions (or reminders of older ones I've forgotten). What would be good and fun to read in this way? Anyone? Anyone? Bueller?