So I had this fun little idea the other day. I tend to stick to reading "classics", because I'm book-snobby like that, but every once in awhile I get talked into reading this-or-that best-seller. Because I hate throwing books away, and anyone who works in libraries knows that donations are not always looked so kindly upon by poor, over-worked, underpaid cataloging and acquisitions librarians, I have a collection of popular reading that I don't really want. Now, I do marketing and outreach for an academic library, but if I was at a public library, I think this would make a fun little promotion:
Hand-write a little note in the front of the book saying something to the effect of: "Enjoy this free book, courtesy of *** Public Library! When you're done reading it, please leave it someplace for someone else to read and enjoy!" Get stickers or stamps made with your website/facebook/twitter/blog on them, and put that under the note. In the back of the book, make a space for people to sign/date/leave a note. Leave the book on a bench outside the library (or even in a public park.)
You can then create a blog, where there's a post for each book, with a little book review. Invite users to post comments about the book, and where they found it/left it. Perhaps even have the sticker/stamp you put in the book say: "Read reviews and track this book's journey here!", with a link to the blog.
If you're worried about your constituents being mad that you're "just giving books away! with taxpayer money!" You can head the blog with a post detailing the program, and explaining it only uses *donated* books.
I don't know if the program would get any traction, but if you've got donated books (or your own unwanted books) laying around, it would be pretty easy to give it a try...