Musée du Louvre (english) open from 9 a.m. to 6 p.m. every day except Tuesday & some holidays, until 10 p.m. on Wednesday and Friday evenings (check the web site opening hours) - the site current exhibitions is not always up to date (like now !) ... better check my link Current Exhibitions above
Musée d'Orsay, famous impressionist collection, also in english and spanish
Musée Marmottan, smaller and quieter, nice Monet collection, also in english (spanish is planned), open 10 a.m. to 6 p.m. every day
Musée Jacquemart André, also in english (with some music), open 10 a.m. to 6 p.m. every day
Musée Luxembourg (also in english) very good reservation web site (for all times) - open every day, Monday, Friday from 10:30 a.m. to 10:00 p.m. Tuesday, Wednesday, Thursday, Saturday from 10:30 a.m. to 7 p.m., Sunday from 9:30 a.m. to 7 p.m.
Musée du Petit Palais de Paris - free entrance for permanent collections - open 10 a.m. to 6 p.m. except Mondays and holidays, and until 10pm on Thursdays for temporary exhibitions
Musée Maillol (also in english), open 11am-6pm except Tuesdays and holidays
Musée du Moyen Age - Thermes et Hôtel de Cluny
if you like modern art
Musée d'Art moderne de la Ville de Paris open, Tu-Sun 10-18h, We 22h
Centre Pompidou, open 11am-9pm except Tuesdays
if you like arts from Asia
Musée Guimet (also in english), good in art from Asia, open, Tu-Sun 10-18h
Musée Cernuschi musée des arts de l'Asie de la Ville de Paris, 7 avenue Vélasquez, 75008 Paris, Ouvert tous les jours sauf lundi et certains jours fériés de 10h à 18h, Entrée libre et gratuite dans les collections permanentes Métro : Monceau, Villiers, Bus : 30 et 94
if you like arts from Africa, "arts premiers"
Musée Quai Branly and Information page open tuesday, wednesday and sunday : 11am . 7pm, thursday, friday, saturday : 11am . 9pm
Musée Dapper (english) current exhibition We-Mon 11-19h. African art ++++, nice cafe
if you like history
Musée Jean Moulin Tue-Sun 10-18h