Joy of Cooking

This cookbook is one of the most comprehensive cookbooks available. Often it is called the "Bible" of cooking. Although it includes an extremely wide variety of recipes, what makes this book so good is its explanation of cooking techniques. It also explains the background of the recipes and the proper way to follow it. For example, rather than listing all the ingredients and then telling the reader the instructions, it says first to bring all ingredients to room temperature, then beat two eggs, cream with a cup of butter, etc. For some recipes this can be pedantic, but for more difficult ones it makes the difference between a mediocre and a fantastic dish.

Wikipedia also has a brief, but interesting article on Joy of Cooking. You can get the classic Joy or the new version at Amazon.