This Saturday, the 7th, is the Friends of the Bend Library Fall Book Sale. They have "Thousands of books of all kinds for sale: fiction, nonfiction, travel books, children’s books. Music CD’s and free books too!" It’s taking place at the Library Administration Building (507 NW Wall Street, just down from the main library building) from 10am until 4pm.
These are usually pretty good sales; the quality of books you’ll find at one depends on both how soon you get there and what you’re looking for. So get there early! And the deals are unbeatable, too. I’ll definitely try to make it.