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.
Small Space Secrets: Swap Your Bookcases for Wall Mounted Shelving. Here's a creative shelving arrangement that uses a deeper shelf at bottom to create a sort of bench. The bench can serve as extra seating for parties, or as a display space.