Museums

Most museums are closed on either Monday or Tuesday, but are open on Sunday.

Musee d'Orsay Musée d'Orsay, 62 rue de Lille, 7th arrond. (the entrance is from a square adjacent to the quai de Solférino, across the river from the Tuileries garden). A transformed railway station which houses the Impressionists' collection which used to be in the Jeu de Paume museum, as well as an impressive gallery of 19th century sculpture, and a section on the architectural history in Paris. The inside view of the building itself is almost worth the visit. Closed Mondays.
Musee Rodin Musée Rodin, rue de Varennes, near Boulevard des Invalides (métro stop Varenne). The original "Gates of Hell," plus a stand-alone version of the "Thinker" are in the courtyard. The museum is housed in the splendid architecture of the Hôtel de Biron (a "hôtel" simply meant a private mansion during the 17th and 18th centuries) and the gardens are an oasis of peace in the middle of the city. Only the view of the Invalides dome and the Eiffel Tower above the hedges are a reminder of the surrounding presence of Paris.
Musee Picasso Musée Picasso, 5 rue de Thorigny, 3rd arrond. If you like Picasso, this will give you a good retrospective of his life and work. If you don't like Picasso that much, it will give you an indigestion. The museum was established with works of art that the artist's family gave to the state as payment for inheritance taxes. There is a suspicion that they donated inferior work in order to get off lightly. While there may be few of Picasso's masterpieces among these works, as I said it gives you a good overview of his entire oeuvre.
Le Louvre ... and the Louvre, of course, especially since now, at last, you can find the entrance! It's through I.M. Pei's glass pyramid in the center of the complex. There is an alternate entrance (sometimes less busy) from the subway station Palais Royal. If Mona Lisa's smile leaves you cold, try the Egyptian rooms, and also the new, immense, very well-lit sculpture halls in the Richelieu Pavilion (the north wing of the building). And don't try to see everything in a single visit.