built-ins are the ultimate bookcase luxury, and my favorites are designed by architect hugh newell jacobsen. jacobsen [pictured at top} builds floor-to-ceiling walls of his signature bookcases into his all white, flooded-by-sunlight interiors. the nearly paper thin shelves are called "egg-crate cases", based on the design of antique wooden egg crates [see bottom image, above]. this means there is a basic outer frame to fit the wall recess, filled with slotted horizontal shelves that are then fitted with slotted vertical supports. he explained: “You are always taking books off the shelves and the rest all fall down... With this design, you can remove a whole foot and they won’t.” while these shelves are not commercially available, plans can be found here.
if you want a similar look ready-made, german company interlübke manufacture the studimo system [below], which promises to fill "the entire height of a room down to the last millimeter". studimo is not as thin and elegant as the jacobsen egg-crates, but at least you won't need a carpenter.