I’m a sucker for books marked “annotated edition”, “critical edition”, and sometimes “definitive edition”. Here’s an article on a new edition of Huckleberry Finn. U.C. Berkeley researchers studied the original manuscript and Twain’s letters to try to undo the work of well-meaning proofreaders and typists’ errors. Other critical works I’ve made note of are The Annotated Alice, which is wonderfully done by Martin Gardner, The Annotated Wizard of Oz, which I haven’t taken a close look at yet, and The Diary of Anne Frank: The Critical Edition, which I’m waiting for a cheaper copy of; in the meantime I’ve got The Definitive Edition.