If Julia Child's Mastering is like a very good undergrad course in French cooking, then Paula Wolfert's The Cooking of Southwest France is a wonderful graduate education in a particular region. For a simpler and easier approach to French cooking at home, why not try Anthony Bourdain's cookbook or one of Julie Child's simpler cookbooks? I've generally had good luck with recipes from the Bourdain cookbook, especially the onion soup recipe.
Fergus Henderson's two cookbooks are wonderful to read and have some interesting recipes, especially if you like offal. I roasted a suckling pig this weekend, taking some suggestions from recipes in Child's and Henderson's cookbooks, and I was quite pleased with the result.
For other baking cookbooks, have you ever seen any Francois Payard or
Pierre Herme' cookbooks? Herme's recipe for chocolate macarons is definitely worth trying.
For Cajun and Creole cooking, books by Paul Prudhomme and John Folse are worth a look. I've found both of them to be helpful, even in law classes: my only book award came about because of a seminar paper in which I set the Hart/Fuller debate in the context of gumbo.
I don't find Ina Garten's cookbooks to be worth the price, especially since you can often find her recipes on line. They make nice coffee table books and the recipes aren't bad, but there are so many more interesting books out on the market.
Thank you, Friend of Belle!