First the "not": a little book I made of Arches 90lb. paper, with a scrap from an unfinished painting as the cover/accordian binding that holds the signatures in place.
The directions for this "Flat-Style Australian Reversed Piano Hinge" book are in Gwen Diehn's excellent Real Life Journals: Designing & Using Handmade Books.
You make an incision in the fold of your signature, then slip the accordian pleat through. Glue down the covers and voila.
This a small test-run, 3 x 5 inches; I'd like to make a larger one.