Thérèse de Dillmont Encyclopedia of Needlework. I have my mother's copy of the book but was delighted to find it online. The illustrations are so clear. I see they have now included instructional videos too.
ENCYCLOPEDIA OF NEEDLEWORK By Thérèse de Dillmont - Vintage Needlework online book with a large section on crochet. It uses old terminology, but if you can figure that out there are some great illustrations of the stitches, and some complex patterns.