A bit about me:  My whole family reads...a lot.  So, what I tend to try to list are used books that we no longer need (or that we have extra copies of).  What you ought to know is that books in this house are well cared-for and usually in excellent condition.  Ripped pages, torn covers, bindings that are bent out of recognition...these are things that all of us frown on.  When we borrow books from the library, even my six year old gets upset if someone has written in or torn a book.  It's a big no-no.  Also, we are a non-smoking house, so our books are nice and clean in that way, too.  I'll sometimes list movies, too.