Great Source for Modern Bookshelves
It's always a good idea to start with someone that is obsessed with books and modern shelving. Enter Erik Heywood who runs Books At Home, a blog about books, or rather, about how to store them. He rounds up simple modern shelving pieces that are astronomically expensive, and then hints at versions you could do yourself.
This Eiermann Shelving was originally designed by Egon Eirmann for a home he was creating and is now mass produced in Germany by Richard Lampert. But with simple materials and some technical know-how, you could build your own.
Supersystem Shelving by Tom Khune is a series of interlocking boards that make a low profile system for paperbacks and small objects.
The top image is of shelving designed by Mogens Koch which get their durability from dovetailed joints which reinforce the thinner than you'd expect modular walls of the system.
See more examples and sources for modern shelves on Books At Home.