These are the cookbooks that I think should be the foundation of any kitchen. Those who don't eat meat: hang on for the special vegan section at the end
1. The Way to Cook by Julia Child. I have Mastering the Art of French Cooking, and it's marvelous, but this is the book I open most often. This is the guide to cooking the things almost everyone wants to make, perfectly.
2. Essentials of Classic Italian Cooking by Marcella Hazan. There are newer, hipper Italian cookbooks out there, but when all's said and done, I turn back to Marcella. There's something about her seventies sensibility that I actually find very soothing; her recipes are neither showy, nor designed to be made in ten minutes between IPO teleconferences.
3. I'm Just Here for the Food and I'm Just here for More Food by Alton Brown. Oddly enough, I don't particularly care for most of his recipes. So why do I own both of his books, and recommend them to everyone? Because Alton Brown explains food better than anyone. His books go over the chemistry and explain the concept of what you're trying to do, which equips you to go out and deploy (or modify) your own favorite recipes more successfully. One small example: he's the reason I bought an electric griddle to cook pancakes at exactly 350 degrees, which produces a perfect pancake every time.
4. Fast Food My Way and More Fast Food My Way by Jacques Pepin I cannot overstate the excellence of these books. They stand alone in the genre of "Things I can make quickly after a long day of work". Most 30 minute meals are designed to be consumed in front of a television in five, and could as easily replaced by triscuits and low-fat Alouette with a Pop-Tart chaser. Jacques Pepin's recipes are not merely things you can make, but things you should make, and will make even when you have time to kill.
5. The Betty Crocker 1950 Picture Cookbook is not merely a fine bit of kitsch. It is actually a pretty reliable guide to cooking American staples, from meatloaf to macaroni and cheese. My mother, who turned herself into a pretty reliable gourmet by way of classes with folks like John Clancy and Craig Claiborne, and actually did a stint as a caterer, cooks a surprising number of meals out of this book. It's ordinary American cooking, really well done, from an era before salad oil replaced butter, and health replaced flavor.
6. The Gourmet magazine cookbook I've never been able to get into The Joy of Cooking; somehow, it's sensibility of comfortable shoes and stuffing olives into the gaping maw of Midwestern ennui oppresses me. The Gourmet Magazine cookbook fills the role in my cupboard that Joy fills for many other folks: there's a recipe for damn near everything. And I haven't found a bad one yet.
7. Julia's Kitchen Wisdom by Julia Child This is an odd little book; it's basically her tips and tricks in the kitchen. But it's invaluable. From who else would you learn to simmer rice in a tomato soup, and then puree, to get cream of tomato soup without the fat? Or hardboil an egg absolutely perfectly, every time? I especially recommend it for the new cook, but almost everyone will learn something.