Julia Child, The Way to Cook
If you only buy one cookbook, and you'd rather learn to cook than look up particular dishes, this is the book to get. The Joy of Cooking has more recipes but won't teach you as much. In The Way to Cook, Julia Child has distilled and modernized the techniques and recipes of her other books. You'll find French classics like Coq Au Vin, Puff Pastry, and French Bread, but the book has an American feel. There's even a recipe for New England Corn Chowder. The pictures are decorative enough to inspire, but with enough shots of Child's wrinkled hands in action to help you through the complicated recipes. The chapter on bread is particulary thorough. As are the directions for a Duck Pâté Baked in Its Own Skin, which Child assures us, is nothing more than a “dressed-up meat loaf”.
The Way to Cook is arranged in traditional chapters (Soup, Poultry, Meat, etc.), but within each chapter, recipes are grouped by method of preparation. Leg of lamb follows roast beef, for example, and all the braised vegetables come together. This arrangement allows Child to spend more time on technique – ideas that apply to more than just the recipes in the book. She also explains many common tricky recipes (like soufflés, hollandaise sauce, caramel, and omelettes) well enough that you'll be able to make them without the book.
The only section where you might find yourself wanting another cookbook is in the desserts. Those chapters seem more French than the rest of the book, despite several recipes from old American cookbooks. There aren't any chocolate chip cookies here, or an apple pie (I don't count the apple tart). Still, you can have fun making truffles, meringues, caramel custard, and, if you're feeling ambitious, a bûche de Noël.
Despite all that, if French cooking is what interests you, I'd recommend Mastering the Art of French Cooking over The Way to Cook. It seems more authentic, and it's more comprehensive. But if you just want to learn to make good food with French flair, The Way to Cook is the way to go.