We were only in Paris for 7 days, but we do have a few favorite restaurants:
L’As du Fallafel (Marais)
Sandwiches at the walk-up window or seating inside. Fantastic falafel, hummus, eggplant, fries, etc. We ate here twice during our visit. Yelp. Wiki. NY Times.
Le Petit Cler (Rue Cler, 7th ARR)
Bistro with wonderful food. Make a reservation for dinner. We ate here twice during our stay also. Website. Yelp.
Le Cafe du Commerce (15th ARR)
Traditional French brasserie with a great classic poster collection and amazing food.