I have nineteen white Ikea Billy Bookcases (the narrow ones) with the toppers and glass doors. These bookshelves (about 16 inches wide) are narrow enough to keep books from looking sloppy from falling on their sides and are only 11 inches deep. People always ask me if the bookshelves are built-ins as they span both living room and dining room without sacrificing floor space. The glass doors really add to the effect, although they did cost more than the bookcases. We recently moved to a larger home, but this is the same number of bookshelves that we had when we lived in our 900 square foot home for 8 years with 7 children. My husband supports my addiction for used books from our friends of the library sales. :-)
And I love my wall that is entirely painted with chalkboard paint.