Ship in bulk to poor countries for use as bricks. There's clearly no other profit to be had for them.

Sell them?

Old books have essentially no value. Cracked (of all places) did a story of how hard libraries work to get rid of books, and all the problems that they face just trying to even put them in the trash.

http://www.cracked.com/article_19453_6-reasons-were-in-anoth...