I wrote a whole post about swapping your bookcases for wall-mounted shelving. Wall-mounted shelving takes up less space, and can almost appear to blend in with the wall. Image from Stadshem, via Freshhome.
A 606 Universal Shelving System by Dieter Rams for Vitsœ is the perfect perch for a color-coded array of books in this midcentury L. Photo by Spencer Lowell. This originally appeared in Modern Renovation of a Midcentury House in Los Angeles.