Having spent several months in New Delhi, I'll give you my take on eating out there. As in most Indian cities, dining out is still a bit frowned upon, though this is changing as the cities modernize, meaning that Mumbai, and then Bangalore, have the most interesting dining and night life opportunities. Therefore, the best Punjabi cuisine in Delhi is not to be found at the restaurants, but at homes. And certainly there is not much good ethnic/global cuisine to be found there, except maybe the Tibetan and Nepalese immigrant-derived options.Street food can also be an interesting affair in Delhi, but you need to be very careful about that throughout all of India. It is one of the few places in the world (and I have been to many third-world countries) where I am very circumspect about eating on the streets (let me know if you survive a pani puri encounter).
Old Punjabi standbys include Moti Mahal, where murg makhani, a sort of alfredo-like butter chicken, was supposedly invented, and Karim's (Mughlai). For haute cuisine, Haveli and Bukhara are oft-cited, though I think they are a tad overrated, and both expensive even by Western standards.
What do I recommend for the visitor? For great South Indian veggie food, try Sagar Ratna, which has outlets all over the city and will run you US$2-3. Chor Bizarre (Kashmiri) and Punjabi By Nature offer good veg and especially non-veg options and will set you back about $10 (both have locations in London, by the way). For a splurge, and one of the few modern/fusion options, try Masala Art, which cooks everything in olive oil rather than ghee. Mark Bittman, the Minimalist, agrees with two of these choices. There isn't a standard dining guide for all of India. The Hindustan Times Dining Guide is good for Delhi and Kingfisher Explocity is good for Bangalore. Both are available in bookstores.
