SendBooksToInmates tells you how to buy and mail a paperback book to any prison through a book provider. From the site (except I fixed a tiny grammar error):
isare currently more than 2 million people incarcerated in state and federal prisons in the USA. Prisoners need books to help pass the time and try to educate themselves. At many prisons there are very few books available to the prison population, and often what is there is poor quality pulp fiction like romance novels and action thrillers.
It was that last sentence that killed me, this day before the day before Christmas. Romance novels and action thrillers? I bet they also have a lot of copies of Tuesdays With Morrie. Oh holy night! So I included the link for anyone who wants to take a break from your relatives and be able to say "Leave me alone, I'm sending things to guys in prison!"
Oh, comment with what books you would send to someone locked up in prison? Three I would send: What Remains by Carole Radziwill, The Education of Little Tree by Forrest Carter and The Way of Zen by Alan Watts.