Books, books and more books! I've always wanted to have a high-ceilinged room with books from floor to ceiling. so high in fact, that you need one of those slidey-ladders to reach the uppermost shelves.
Idea for when we put french door in dining room. Ikea Shelves Into Built-in Bookcases :: I really love this. You could turn any room into a library with this idea. And you don't need ikea for it, either.