If you are just starting out, the one cookbook that you must have is Joy of Cooking. It has recipes for anything and everything--meats, casseroles, pickles, jellies. If you want to cook it, Joy will tell you how. Additionally, it is a gold mine of information on cuts of meat, measurements, substitutions, even how to set a table. Other cook books have celebrity chefs, but Joy has time-tested recipes and advice.
For Italian, I think that Marcella Hazan is a genius. Classic Italian Cooking would be my choice. Every recipe is delicious and usually deceptively simple. For French, I love Julia Child's Mastering the Art of French Cooking and Simca's Cuisine by Simone Beck. I like Martha Stewart's Christmas Book and Maida Heatter's book about cookies. (Miss Debbie has her Cake Bible which she likes a lot.) For Cajun and Creole cooking there is nothing better than Cajun-Creole Cooking by Terry Thompson. Most cookbooks will have one or two recipes you like. Everything that I've cooked from this book is fabulous.