Hogwarts: An Incomplete and Unreliable Guide by J.K. Rowling, 121 pages
Short Stories from Hogwarts of Heroism, Hardship, and Dangerous Hobbies by J.K. Rowling, 112 pages
Short Stories from Hogwarts of Power, Politics, and Pesky Poltergeists by J.K. Rowling, 110 pages
This trio of short books were released as ebooks earlier this year through Rowling's official fan page, Pottermore, and each provides additional insight into the meticulously created wizarding world Rowling created with her Harry Potter books. Included are short stories about favorite characters from the original series (I particularly liked the story of Professor McGonagall's life before meeting Harry), as well as additional information about magical artifacts and processes (how the heck Peter Pettigrew ever became an Animagus, I'll never know). As a bona fide Potterhead, I loved these books.