They used to be $1.00 a piece - now they're about $2.50, but still a great deal! Hardcover books from Goodwill are an inexpensive way to meaningfully accessorize a bookshelf.
I usually look for classics or popular novels that don't have words like "Angel" or "Devil" in the title. Remove the covers - be sure the bindings are neutral or useful colors such as black, tan, even red.
It's good if they're the same height. However, big picture or coffee table books can add some drama.

If you can't find the "right" books, just buy what they have - and cover them! Subtle gift wrap, brown kraft paper, even fabric will work as bookcovers. In these examples, I covered the books with newspaper - the black on white fine type and columns of numbers provide some visual interest without making you want to pick up the book and actually read it - that would be distracting - and this is Staging, after all!
Some of these books are novels, others are cookbooks and children's books - they come in all sizes, so don't overlook them.
Happy Staging - Julie
Nestings provides high-quality, value-added staging for occupied, vacant and model homes in Fairfield County and Connecticut.
Julia Vigneron Maher, Nestings: Award-Winning Staging for Model, Vacant and Occupied Homes in Fairfield County, CT and Connecticut.
Hmmm, an interesting thought. I like it as long as the books don't all look alike. Leather covers are nicest, in my opinion.