Here are some contenders I've recently checked out of the library:
Patternmaking for Fashion Design (4th ed.)
by Helen Joseph-Armstrong
This hefty volume looks like it is the most comprehensive of the three. It shows you how to make a sloper from measurements and provides 800 pages worth of instruction on manipulating the sloper to create a seemingly infinite array of design possibilities. There is even a section on creating swimsuits.
Cons: Very pricey! Used copies start at $109.95. Also, a few reviews point out some errors.
Principles of Flat Pattern Design by Nora MacDonald - Looks similar to the Joseph-Armstrong book, but less comprehensive. The illustrations are plentiful and clear, but it doesn't seem to cover coats and jackets or other garments outside the basics. Nevertheless, it's gotten some good reviews and is significantly less expensive than the Joseph-Armstrong book.
Professional Patternmaking for Designers by Jack Handford - This one also covers the basics of sloper construction and manipulation, but at first glance the instructions don't seem to be as clear as the other two books. The book does cover pattern grading, though, which is on my long list of skill to acquire.
What are your favorite sewing books? Do you have any patternmaking books you can recommend?