The America's Test Kitchen Family Baking Book I'm a big fan of ATK. I don't always agree with their assumptions, but they're recipes are always well tested. A good place to begin any recipe research.
James Beard's American Cookery This is James Beard's masterpiece. Just about anything you want to know about traditional American cooking and its history.
JOY OF COOKING This was a gift, and a welcome one. I use the 1975 edition, but I would trust the 2006 edition. Again, an important source for traditional American cooking.
Baking with Julia: Savor the Joys of Baking with America's Best Bakers I love this book, and it's quite cheap now. I don't necessarily love the butter cake recipes, but the Lemon Loaf is a go-to cake for me. It us also very strong on pastries and breads. If you cook through the book, it's a great education.
The Quick Recipe Since I bought the Ring bound ATK series, this is one of the only single-subject ATK books I kept. This is the original source of the Best Pumpkin Muffins Ever and No-Bake Cheesecake. It has several more quick and very yummy baking recipes.
CookWise: The Hows & Whys of Successful Cooking, The Secrets of Cooking Revealed This is a new book, and I've only made a couple of recipes from it: Touch of Grace Biscuits and All-Time Favorite Sour Cream Cornbread. They were both amazing. Very well organized and written (sadly, better than the more recent BakeWise).
I make a very small amount of money if you buy the books through these links, but don't feel pressured.