I recommend restaurant La Marmite, 2 Boulevard de Clichy | PARIS 18 - it is in the heart of Pigalle. You can sit by the table on the sidewalk or inside in area with opened wall and watching atmosphere of sin. :) Best time is dinner, the quarter begins to live.
The "Best of" salat - big bowl of fresh vegetables, upper is lot of baked potatoes with garlic and top is variable by wish: salmon, duck, frutti di mare, bacon, french ham, vegetarian choice, egg...fabulous! Not expensive, stylish interior and furniture, fine staff.
And second tip is "parisian must have" - cafe Angelína on Rue Rivoli (near Le Louvre). There are prepares "densest chocollate on the whole World" :) Do you have a cup of hot chocolate and you have to dilute the cream because do not even get out of the cup.