Not a cookbook -- but I'm very fond of Manjula's recipes at
http://www.manjulaskitchen.com/ She's put together several videos available on You-Tube and they really help with understanding how to use spices or seasonings that are not used outside of Indian cookery.
Also Indira's recipes at
Mahanandi.
Whenever I'm in the mood to cook one of my favorite Indian dishes, I turn to one of these sites -- and follow links.