Can't help you with the first two, specifically - dh isn't into Mexican or spicy foods.
My favorite cook books overall though are:
Alton Brown: I'm Just Here for the Food; Back for More Food; Gear for your Kitchen (3 books) - the first is cooking methods, the second is baking methods, the third is about kitchen organization/utensils etc. He covers techniques, some basic recipes but more the "why" behind using particular ingredients/techniques.
Baking:
Laurel's Kitchen Bread Book - good information about how bread is made, works, etc.
King Arthur Flour Company's Cookbook (excellent info, again)
I like many of the recipes I use from the Pillsbury's Book of Baking, but the binding is lousy.
Perhaps my favorite overall is a book called The Butte Heritage Cookbook. It's available from Uptown Books in Butte, MT and was first printed in 1976. Ethnic recipes from all over the world, for making food from scratch (I want to make their chicken ravioli recipe, it's a two-day process).