There are apparently 479 art galleries in France! Art lovers who want to see art while in Paris (other than the Louvre!), and all for free, I suggest taking a stroll through the art gallery districts and popping in to check out the works on display.
One can find these art galleries in the following four districts: Beaubourg-Marais, East Paris/Bastille, Rive droite-Matignon et Rive Gauche. I personally walked around the ones concentrated in the Bastille area.
Most of these galleries are promotion galleries (as opposed to traditional) displaying contemporary and avant-guard art. These galleries expose some very cool modern and classical collections of art by both local and world-famous artists.
One of the most famous of these promotion galleries is that of Emmanuel Perrotin located at 76 rue de Turenne in the 3rd aarondissement and Galerie Jean-Luc & Takako Richard which apparently during fashion week, plays home to Karl Lagerfeld's collections - this one is located right next door (3 impasse Saint-Claude, 74 rue de Turenne). I also checked out the Eva Hober Gallery which displayed some very original work of artist Michael Schouflikir (small scale, big message figurines). My 2 favourite of his works on display is one titled 'Panoratma' - a figurine of a small rat sitting on a ridge admiring the view with his bicycle parked nearby him. The other is titled 'Ca Va Trop Vite' which is a figurine of a snail with boeing engines attached to each side of its shell. This kind of tour is ideal for a chilled afternoon while taking in a whole lot of culture!