We had only three days in Paris, so we used Joan von Ohlen's concierge service, offering "customized itineraries for independent travelers." Von Ohlen, an American living in Paris, recommended little-known museums and hidden parks, arranged a fascinating small tour on the French Revolution and introduced us to Paris' best macarons. She found us a hotel and great restaurants in a charming neighborhood. Flexible, fascinating and reasonable.
Joan von Ohlen, Joan's Personalized Paris, http://www.personalizedparis.com. Daily itineraries from $150.