I always try to finish a chapter before I lay down a book. If you are unable to do this, this might be a nice gadget for you. The gadget of today is called Book Darts. These page holders might also come in handy when you want to mark a certain passage or quote in a book. Or when you study and need to remind yourself of important passages in your text book. Learn more about Book Darts here.
Thanks to Mark for the link!