I was Delhi for 10 days last month, and since people on the board made some helpful suggestions (few of which I was able to follow!), I am reporting back.
Some general impressions:
*Ground meat kebabs rock!!! I am generally bored by ground meat kebabs in NY, but in Delhi they were uniformly amazing: extremely juicy (I would not be surprised if they were 30% fat!) and sang out with flavor ginger, garlic, black and red pepper and cumin. On the other hand, grilled pieces of meat were generally overmarinated, to my taste, perhaps to tenderize them. The ground meat kebabs were excellent wherever I had them, home or restaurant, whether of chicken or of lamb, and were generally served with sliced red onion. My favorite was probably when they were served in roomali roti, a thin soft floppy bread far superior to the horrid wraps we get here.
*You can do lots of stuff with paneer (Indian cheese). It makes great koftas and pakoras. Best of all, it can be stuffed and grilled in a tandoor. This was served on almost every vegetarian thali that I ordered, and it is great.
*Vegetables were amazing. I ordered vegetarian thalis on several occasions, and was often served vegetable dishes that you rarely get in the US greens cooked in mustard oil; lotus root with greens or other vegetables; jackfruit (think of a tastier version of fried artichokes Roman style); pumpkin with coconut; creamed black lentils (urad dal).
Some restaurants to recommend:
Haveli, in the Taj Mahal hotel, was excellent. Favorites there were a the stewed morels; the grilled vegetable and paneer appetizer; roghini gosht, a lamb stew with lots of paprika and garlic (think lamb chorizo!); and a dish of spinach with fresh corn and shredded ginger. I was surprised that a hotel restaurant was so good, and had some of the tastiest room service ever.
Bukhara, in the Maurya Sheraton, had excellent tandoori lamb, chicken, breads and vegetables.
Ranpur Kitchenthis is a modest place in the Khan Market strip mall, and it serves an unusual style of northern Muslim food. I was particularly impressed by their Muglai roti, a sort of crisp and fluffy pita, and by a stew of chicken in black pepper sauce that was both creamy and spicy.
I actually didnt get to go to that many restaurants, since many evenings were taken with other events. I had some excellent home meals : a Southern meal with curd rice, lemon rice, sambar, a variety of vegetable stews, and excellent homemade pickles; a northern meal with a chicken cooked with cloves, cardamom and chiles, ground chicken kebabs and many wonderful vegetables; and an evening of kebabs and qawallis (sufi chanting).
My main regret is that I didnt get to go to a dhaba (truck stop) as Howler had recommended. When I mentioned this to one of my keepers, a Bengali, he said "We like you too much, and we wont let you go. I have been here for 3 years and I still cant eat in places like that." It turns out that he is a rather ascetic fellow, but he was so generous that I felt that as long as I asked, I couldnt very well go against him on this. Maybe next trip!