One with lots of vegetarian options. Ethnic would be good. Focused on a cuisine or a place or a time or something. Not technical, not reference, just recipes.
The only cookbooks I have right now are once I use as reference materials When I have a specific question about technique, they serve me well, but they don't inspire me. My library reflects, and maybe informs, my mindset. Over the last half-year or so, I have grown more concerned with technique, theory, chemistry, equipment. I have lost interest in humble, earthy, accessible food, and even begun to dismiss it, in my own mind. A colleague cooked a bacon-wrapped stuffed chicken tender a few weeks ago. On the inside, I sneered at the lowbrow concept while admiring his perfect technique.
I haven't cooked a curry in months.
My cooking at home has suffered, as has my creativity at work. Uninspired, I've settled into a rut of making uninteresting food at home. Sauteed vegetables on pasta again. My technique is much improved: the vegetables are almost perfectly cooked. They are also the same vegetables I cooked yesterday, and I'm bored with the dish. I've gotten used to being bored with the food I make, and now it's hard to think of things I won't be bored with. Most of my own ideas I dismiss as uninteresting, tired.
So it's time for a fresh start. Time to get back to being open minded and exploring delicious peasant food. I need to continue educating myself about technique and theory, but without developing an arrogant mindset than denigrates anything. I think a new cookbook is a good start.