My top three recommendations are:
1. Creating Handmade Books by Alisa Golden has clear, concise text and illustrations for making everything from simple one-page structures all the way up to multi-signature sewn structures.
2. Making and Keeping Creative Journals by Suzanne J. E. Tourtillott is a feast for journal lovers. She offers innovative structures to match topics such as gardening, birding and art journaling.
3. Sleight of Binding by Cherryl Moote offers playful structures to lift your books into the third dimension. You will find kinetic and interactive designs in shapes and colors that wake up your creative mind.
Here are some pictures of my work using these books for instruction and inspiration.
Book/card with tunnel from Creating Handmade Books. (2014)
Jacob's Ladder book (front and back) and content from Creating Handmade Books. (2004)
Jacob's Ladder "Flight" book from Creating Handmade Books. (2009)
Journal with different color and size pages from Making and Keeping Creative Journals.
Inside of journal showing content. (2003)
Dos-a-Dos book from Making and Keeping Creative Journals.
Inside the Dos-a-Dos book. (2003)
Glove book inspired by one in Making and Keeping Creative Journals. (2007)
Gallery Book from Sleight of Binding. I modified Cherryl's structure by leaving the paper on the front of the "windows" and using it to fold the cranes. (2012)
Cherrly's book Sleight of Binding has many kinds of flexigon structures. Here are three that I made using Graphic 45 papers. (2014)