The Annotated Alice, Martin Gardner's astounding edition of Alice in Wonderland and Through the Looking Glass which explained all the mathematico-logical in-jokes and history that Carroll had scattered through the books.
Well, I just found a copy in the "put-a-penny tak-a-penny" bookshelves of my building's laundry room. I will bring down all my thrillers and the Millennium Trilogy in return.
Yes, I'm a massive nerd. We've met, no?