Some major non-chain hotels are the Ashoka, Oberoi, Taj Mahal and Taj Palace. Delhi unlike Bombay goes to sleep early so I am not sure how vibrant these places will be. Taj Palace is located closer to the city center. Taj Mahal and Ashoka are closer to the airport (10 miles) near the Diplomatic Area of Delhi. I think $200 a night should find you a decent room in these hotels. The Ashoka is run by the govt. and has a more traditional architecture. However I am not sure how the service levels would compare with the privately hotels. Taj is one of the biggest chain of hotels in India and in general you should expect high service levels.

There are a number of other smaller hotels near the City center which can offer a different atmosphere.