If your home is starting to bear a strong resemblance to the bookstore around the corner, 1. I'm jealous, and 2. here's a unique way to acquire some additional storage.
The idea of getting rid of even one book pains me to no end. So head for the rafters and get creative!
When space is at a premium, look up. Consider all of that unused space near the ceiling. This designer has books literally hanging from the rafters, with a ladder conveniently placed for easy access.