I love cookbooks. I haven't counted recently but I probably have close to 50 of them. Not all of them are big ones. I have lots that are thin booklets from a variety of sources (a Pennsylvania Dutch one, English cooking, dutch oven cooking, etc). But I do have my favorites. I use my 'Joy of Cooking' a LOT. It was a gift from my Mom when I moved away from home 25+ years ago and is showing it's age. The spine is cracked, the cover ripped, the dust cover was destroyed long ago and it's definitely not the latest edition. But I still treasure it. It has lots of information about a great variety of foods and cooking techniques in addition to recipes.
Another couple of favorites are from the Mennonite Central Committee. When we lived in Pennsylvania, my MIL got me this great one called 'Extending the Table... A World Community Cookbook'. It is a collection of world recipes from missionaries with lots of tips for frugal living and cooking since most of the world eats much more frugally than do we here in the US. It's fun if you want to have an African or Latin American meal.
And speaking of frugal cooking. A few years ago I treated myself to the 'More-with-Less Cookbook'. It is wonderful!!! It is worth the read even without the recipes! It has information on substitutions, complementary proteins, comparison of protein costs (not recent) and so much more. I also love it because of the attitude it promotes: That we need to do more with less, to be good stewards and not take more than is our share. It's definitely worth checking out from your local library if nothing else. It's worth the read.
I have other cookbooks that I use regularly but these are some of my favorites, just thought I'd share.