Here are three of my picks for the best museums in Paris, after the big names like the Louvre and Orsay:

Musée Marmottan
Métro: Muette.  Bus: 32.
Museum Pass: No – admission is €10.  Closed:  Monday.  Open late Thursday (7:30 p.m.). 
A museum containing some fabulous works of Impressionists, especially Monet, featuring his early works.  One of the best kept secrets in Paris.  A comprehensive collection of Monet’s paintings are displayed in a relaxing atmosphere, quite different from what is found at the Orsay.  Impressionist art lovers should not miss this museum.  A little bit out of the way.  No photos.  About 90 minutes to 2 hours. Website: www.marmottan.fr.

Musée de l'Armée (Army Museum) 
Métro: Varenne or La Tour Maubourg.  Bus: 28, 82, 92.     
Museum Pass: Yes.  Open late Tuesdays April-September.
A museum dedicated to the French military.  Military uniforms, weapons, and equipment from all eras of French history dominate this collection.  The WWI and WWII exhibit is of great interest and shows how De Gaulle won WW II.  Can a mention of FDR be found?   There is also a sobering exhibit on the horrors of the holocaust.  1 ½ hours.  Website: www.musee-armee.fr/en/english-version.html.

Musée des Arts et Métiers
Métro: Arts et Metiers. Bus: 38, 47, 75.
Museum Pass: Yes.  Closed: Mondays.  Open late Thursday.
Paris is well-known for its contributions to art, cuisine, and humanities. But let’s not dismiss a rich legacy in the fields of science, mathematics, engineering, and technology.   The 80,000 item collection of historical artifacts here is impressive.  For instance there are sound recording devices by Edison and a French airplane pre-dating the Wright Brothers along with early automobiles, TV’s, computers, engineering and technology marvels.  It is one of my favorite museums in Paris.    About 2 hours.  You would think they would have a better website though:  www.arts-et-metiers.net.

For more information on The Traveling Professor's tours to Paris, see www.travelingprofessor.com