Some books are best for certain parts of the country, esp for foods that grow there (mostly) exclusively, like the warm South.
Along with Carla Emery's Encyclopedia of Country Living, the catalog of books offered by Storey Publishing (on many useful subjects, not just cooking) at http://www.storey.com/
To tell the truth, I've found that the usefulness of cookbooks can be determined rather severely by personal preference. One entry that tells you to do something that you KNOW doesn't work, can taint your opinion of the entire book, even though the rest of their info is quite useful.
I only use cookbooks as rough guides so I know what to expect as far as cooking times and things. Such as with a roast (they usually give a poundage and cooking temp) and approx. ratios for things like custards (approx how many eggs per cup of milk? ) other than that they are really just idea generators for me. My favrorite is an amish cookbook because it often has ideas for things to make based on what I can realistically grow or afford as well as uses things with actual calories! which for me is the whole point of eating, its fuel for my body! I can't stand it when I pick up a cookbook and it is full of recipes for lettuce or greens, healthful additions to a real meal but not going to supply me enough calories to root around in the garden throw a pallet of feed sacks in the shed or lug 80lb square bales to the barn. ( the only thing I detest more are cookbooks that call for ingredients like "1 can of cream of mushroom soup and a chicken breast" c'mon who needs a recipe for something like that?)
My second favorite cookbooks are the "best of country kitchen" books. I inherited several when my grandmother passed and found them to be excellent idea generators. No recipe stays intact in my hands though. I usually use the cliche cookbook "better homes and gardens cookbook" for basic ratios and times for things.
the key to cooking is just knowing the basics and then figuring out what to make with what you have on hand or that needs to be used up.
I'm not vegetarian, but for whole foods cooking, especially beans, rice and other grains, my "bible" has been The New Laurel's Kitchen. It is an amazing resource, including a comprehensive nutritional value index in the back. A great read and fabulous recipes. My favorites include: -chile con elote -peanut butter honey cookies - the BEST pb cookies ever! -corn bread -corn pone -slaw chez nous (sp?) -making your own dried herb seasoning blends -Annalee's crookneck chiffon pie (oh, I wish I still ate dairy for this one!) and lots more. Maybe not technically permie, but it's all about whole grains, in season, unprocessed foods from scratch. Especially good when I was new to homemaking and had grown up with the cream of mushroom soup casseroles and hamburger helper kind of food. There's a handy cooking table for whole grains that I refer to frequently.