I have a bunch of cookbooks, but I stopped buying them when I realized that I use them rarely if at all. The ones I do find myself using are:
Cook’s Illustrated Magazine: I have just about every issue published, and the yearly indices. These cover just about anything I’d want to make, clearly and concisely. The recipes always work. The magazine has a good mix of “normal” food - roasted chicken, pasta dishes, etc. - and a sprinkling of “special” dishes that are nice for a Sunday meal or when you have guests over. After relying on these for so long, I find myself getting upset over recipes in cookbooks and other magazines because they never go into enough detail. If I have to dredge the chicken cutlets in precise measurements of Wondra Flour, Panko Breadcrumbs, and expensive Egyptian Wogonza spice, then damn it, I want to know WHY, and I want to hear the other options you tried on the way to coming up with this particular mix, plus I want a mail-order source for that Wogonza spice.
Joy of Cooking: I’m with the others here - this is a must-have reference. I rarely cook from the recipes it offers, though. I’ve found that most of them don’t go into enough detail, or are dated. But if you ever need to know what a particular cooking terms means, or look up the name of that funky fruit you saw at the grocery store, this is the book for you.
Betty Crocker Cookbook, circa 1963: This was one of my mother’s favorite cookbooks, so much of the comfort food I grew up with comes from it. Plus, who can live without the funky illustrations?
On Food and Cooking: Where else can you find pics of the microscopic details of the starch found in flour? Or charts of the most common food-born microbes? Ya gotta have a copy of this, if only to impress your friends.
Misc: A couple books by Marcella Hazan, a couple by Julia Child, a couple by James Beard. Always need a few by the masters. Oh yeah, Johne Thorne, just for fun & light reading.