Also 'Musée National du... by Puffin
Also 'Musée National du Moyen-Age Thermes de Cluny' is beautiful. Everyone who is interested in medieval history can't leave Paris without visting this museum.
The most famous collection of this museum are the 5 wall carpets with unicorn. Each carpet symbolize one of the five senses.
http://www.paris.org/Musees/Cluny/