I think that my favorite is Simply in Season. More-with-Less's extreme obsession with calories and low-fat seems quite dated and Extending the Table sometimes calls for ingredients that we don't keep on hand all the time. But Simply in Season, with its contemporary but delicious recipes is pretty much perfect. I also like occasionally coming across a familiar name in the contributions. There is a chapter for each season, with recipes like Gazpacho in the Summer and Maple Glazed Parsnips in the Winter. I turn to this cookbook quite a bit in the summer. This cookbook also has the added bonus of having an ingredient index. So, if you're being bombarded with spinach, you can look up spinach recipes in the back.
While I don't use it frequently, Extending the Table has introduced me to some delicious recipes. The kimchi is one of my favorites and Shanghai Ham is also wonderful. This cookbook is a great way to learn a little bit about different countries and it's a good place to turn to to replicate restaurant dishes.
I think that I have the most memories and associations tied to More-With-Less. There are some basic recipes like mayonnaise and french dressing that are perfect. And, while low-fat is stressed, there is nothing nasty or flavorless about the food. Even the recipe for Wheat Germ Balls is delicious!
I was surprised and glad that these cookbooks can be found on amazon. I recommend them for anybody who likes to cook and wants a little taste of another culture.