I am really wanting to try the curry cookbook (660).
I LOVE Indian food.
660 Curries is wonderful! It's got very clear instructions and following his method of making rice is the first time I ever got perfect rice in my entire life. Seriously. Everything I've made, including adapting things (subbing coconut milk for cream or yoghurt, oil for ghee &c) has been amazing.
I also recommend Yamuna Devi's Lard Krishna's Cuisine. It's vegetarian but easily adaptable and has a lot of recipes, as well as an awesome introduction to different dals and so on. I feel like it's more complicated than 660 Curries but I also cooked from it first before I'd really cooked much, so my memory might be colored by that!