The Madhur Jaffrey cookbook I use most often is From curries to kebabs (published first in the UK as The ultimate curry bible). I like the breadth of it, because it presents recipes resulting from the diaspora of people from the Indian subcontinent in addition to strictly Indian recipes. But because of that, it might not be what you are looking for.
I was going to second robm's recommendation of Flavors of India, then realised that the book on my shelf I thought was Flavors of India is actually called A Taste of India. Very confusing. And it doesn't help that many of her books have been published in the UK and the US with different titles.
I would recommend A Taste of India as a nice survey of recipes from the different regions of India. That way you would get an idea of the spectrum of Indian cuisines.
Unless you have a pressure cooker and are not afraid to use it, I would not recommend the Quick and Easy Indian cooking--the recipes seemed to me to take some unecessary shortcuts and relied heavily on the use of a pressure cooker to cut down on total cooking time. But for me, one of the glories of Indian food is the depth of flavors achieved by slow cooking.
I see that she just published a new book in the UK called Curry Easy which might be even a better one to start with, but I cannot personally vouch for it and it is not yet available in the US. But if you aren't in a hurry to start your explorations, it might be a good choice.
And a final word of encouragement--don't be dismayed by the length of ingredient lists when you browse Indian recipes! they can look overwhelming, but the payoff is worth it.
