The Great Book of French Cuisine a.k.a. Modern French Culinary Art, by Pellaprat.
Although there is a modern edition edited by Jermiah Tower, the older editions are better. It's an incredibly illustrated, incredibly inclusive cookbook. It has more than 2000 recipes representative of the four types of "modern" French cooking: Regional, Bourgeois, Impromptu, and Haute. Although the style is a bit old fashioned, even fussy, the directions are crystal clear and easily followed by a competent cook -- as you would expect from recipes written by the greatest cooking teacher of all time. (Pellaprat was the first truly great teacher at Le Cordon Bleu.) Pellaprat published at about the same time he first retired from Le Cordon Bleu, in the mid 1930's. But the best English translation combined with tons of illustrations and a wonderfully stuffy plating style that is no more was published in the late sixties and early seventies.
Pellaprat was born in 1869 and his early professional career overlapped with the end of Escoffier's. The two knew each other. In a sense this book is the successor to Escoffier's Guide Culinaire, but it is a much greater achievement. The breadth is as great, the scholarship superior, and the level of pedagogy unmatched. If you approach the book with an open mind and a willingness to put yourself in the time it was written, you can get a sense of how modern Pellaprat really was, and how he bridged the classic and nouvelle eras. Also worthy of note is the credit he extended to his contemporaries by naming their own variations on the classics after them. Most people in his position simply reverse engineer and steal the credit. He must have been quite a guy.
If you're serious about learning classic French cooking, this is absolutely essential; and of far more value than the Guide. Do yourself a favor and get one of the Vendome editions from the nineties, if possible, in good shape. If you can't find it, get the Tower edited book. But get it.
Mastering the Art of French Cooking, by Childs, etc. Another classic. Still the best book for people who realize they want to up their game from okay to much, much better. What isn't taught, you don't really need to know.
American Cookery, by James Beard. More than anyone else, James Beard created our modern North American sensibility of simplicity and inclusion. Beard wanted you to enjoy good food as a diner and a cook. He made it as easy as possible, too.
Joy of Cooking. More a recipe collection that a cookbook. An encyclopedic collection of recipes, some with good instructions and some requiring technique going in. The book is constantly updated. Whatever's latest is best. If you don't own Joy, you don't own cookbooks.
Gourmet Cookbook (sets), various editions. These are collections of recipes from Gourmet Magazine. The recipes are well edited and tested. The book has been through several editions, each representative of its times. The book is written for the home cook with an interest in cooking and entertaining. Not for the professional.
French Provincial Cooking; Italian Cooking; Mediterranean Food; Summer Cooking, and generally anything else by Elizabeth David. The recipes are not easy to follow. Heck, the recipes aren't necessarily that easy to identify among the fascinating narratives. Still the best cookbooks ever written by the best cookbook writer. David managed to write compelling cookbooks. Still can't figure out how she did it. Not only that, but she taught the England to care about food. Go figure.
Enough for one post,