Bookmarking Audiobooks on iPod Touch

I am constantly listening to audio books on my iPod. Many books come from the library, so are copied from cd. Needless to say, I can't listen to a whole book at once, so have to do it in installments. Is there anyway, I can bookmark where I left off in a book? Almost every time, I return to continue the story, the iPod has lost my place and I have to figure out where to go. This doesn't seem like it should be a big problem. Is there something easy I'm missing???