Its all about timing. If you happen to visit Paris during the first Sunday of a month, you have the opportunities to visit many museums for free, precisely 23 national museums in Paris, including Louvre, Quai-Branly, Orsay, and Versailles. Since its free on Sunday of each month, try to get up earlier to queue as everyone like freebies.

If you can not visit Paris on that specific day, you still have the chance to go to some nice museums and galleries for free, for example, the Petit Palais, Musée Carnavalet, Maison de Balzac, Maison de Victor Hugo, the Musée Zadkine, and many others are free on all opening days. However, this only aplies to permanent exhibitions, not temporary ones.

You can a list of museums and their addresses in the following link:www.patroc.com/paris/map_museums.html