Whether we publish traditionally or independently with self-publishing, we know our books get listed in the Baker & Taylor database. This is what most libraries use to find new material, and order books for their collection. If having a listing among the millions of books in B&T isn't enough, you can spend a little money for a direct approach. Maybe you thought you couldn't afford to advertise, but ...
For a fee, this firm offers you a listing in their monthly catalog to libraries. As an example, their half-page ad for one month costs $75. If you need a way to reach libraries, and have your book reach a wider audience, take a look at First Chapter Plus.
BONUS: First Chapter also hosts a huge Blogging Authors, a perfect place for you to participate.