I love books about books. Reading about a character reading about a character is such voyeurist fun, especially if both the book, and the book within the book are true, as is the case in Lily Koppel's The Red Leather Diary. The diary in question was written by Florence Wolfson during her teenage years in prohibition-era New York, and her reader is Lily herself.
Lily finds a red leather diary in the dumpster of her apartment building, and quickly develops a fascination with its author and her New York. The Red Leather Diary is a personalized view into New York in the 30's, filled with events large and smaller, and plenty of photographs. If you're in the mood for brain candy; this might suffice.