I have to say I think the Why Bar deserves a spot on any 'best cocktail bars' list. The owner makes some top notch cocktails, including creative and deconstructed cocktails at reasonable prices. It's a real find as far as cocktail bars go in Paris.
www.whyparis.fr/
60 rue Jean Jacques Rousseau, 75001
+33(0)1 40 26 47 63
Google map: bit.ly/kWHZET