Its my dream to have a library ladder in my house someday. Floor to ceiling bookcases offer plenty of space to showcase a vast collection of books. A ladder gives access to books placed high on the bookcase.
For even more storage, consider hanging shelves up high that run the length of the room. You won't loose any floor real estate at all, and you'll gain a lot of storage space. Design Dozen: 12 Clever Space-Saving Solutions for Small Bedrooms