October's recommendation: Sorcery and Cecelia, by Patricia C. Wrede and Caroline Stevermer. Subtitled in some editions as or The Enchanted Chocolate Pot: Being the Correspondence of Two Young Ladies of Quality Regarding Various Magical Scandals in London and the Country.
I suspect this is the kind of book where either you'll fall in love with the characters and tone and narrative conceit and therefore think it's wonderful, or else you'll be annoyed by the characters and tone and narrative conceit and therefore think it's stupid. Ergo, the job of this review will be to help you accurately guess which camp you're likely to fall into.
The conceit of this book is that it was created via the Letter Game. As Stevermer describes it, "The game has no rules, except that the players must never reveal their idea of the plot to one another. It helps to imply in the first letter why the two characters must write to each other and not meet in person." Wrede and Stevermer did it for fun one time, and unlike most people, they actually carried the story through to completion -- and then polished it up and got it published. So the entire novel does, in fact, consist of letters sent between the two main characters.
As a result, the story takes place in London and an English country town during the Regency period, with two interlocking plotlines. The main characters are cousins, Kate and Cecelia, one of whom (Kate) has gone to London for her first Season, the other of whom (Cecelia, obviously) is, for various reasons, having to stay home. This is a fantasy version of the Regency period, of course, with charm-bags and colleges of wizards and (as the title indicates) an enchanted chocolate pot, around which much of the plot revolves.
A great deal of the charm of this book lies in its loving celebration of period detail, in idiom, behavior, and material life. I personally find it delightful; I imagine not everyone would. Same goes for the characters. They are somewhat typed to the style and genre (headstrong young ladies, strict aunt-chaperones, etc.), but if you're likely to be amused by someone being repeatedly referred to as "the odious Marquis," then it's not a problem.
There's a sequel to this book now, titled The Grand Tour: Being a Revelation of Matters of High Confidentiality and Greatest Importance, Including Extracts from the Intimate Diary of a Noblewoman and the Sworn Testimony of a Lady of Quality. I haven't yet gotten hold of a copy to read, so I have no idea if Wrede and Stevermer have successfully recaptured the charm of the original. There are some obstacles in the way of doing so, but I harbor a hope that they pulled it off. One of my few complaints against Sorcery and Cecelia is that there's so little of it. I would gladly have read twice as much. Hopefully the second novel will give me a chance to do so.