At the very top of my list and I do highly recommend this one:: The Entrepreneur's Guide To Sewn Product Manufacturing, by Kathleen Fasanella for anyone who has a desire to go into business designing and producing sewn products for sale either online or off.This book will take you step-by-step through the entire process from idea to production and beyond. The contents of this book will give you an overall understanding of the "Trade" and "How to Plan a Line" along with information on marketing, and production. Detailed information is given on price-points, sourcing materials, definitions and the duties of needed industry professionals, including: Grading services, pattern makers, sample makers, cutters and setting up shop. Forms for costing your products and defining your market are included along with forms, worksheets and production scheduling checklist and pattern template guides.
To help you understand the pattern designing process and know what to expect or to begin your own road to pattern designing, not something to be taken on by the faint of hear, is a great book by Connie Crawford, Pattern making Made Easy
Another great book to help you understand what goes into garment designs and fashion sewing for those of you who choose to sew and manufacture in-house, would be Professional Sewing Techniques for Designers, by Julie Cole and Sharon Czachor
Another good, extremely good book for understanding how patterns work is: How Patterns Work: The Fundamental Principles of Pattern Making and Sewing in Fashion Design
I get a lot of request for making and altering patterns and thought this might help to demystify the process when searching for industry professionals.