I would definitely make tracks for the Caillebotte exhibition at the Musee Jacquement-Andre, featuring the paintings of Gustave (whose other works hang in the Musee d'Orsay across the Seine) and the photographs of Martial. I fell in love with Gustave's paintings some time ago, and now discover that I am equally passionate about his brother's pictures. This exhibition lasts until July 11, so go! Someone who is going to Paris could be nice enough to buy me the catalogue...
Plus the museum itself is a wonderful trip. Buy your tickets ahead of time, and plan to eat lunch in their delightful cafe (again, go early!). They actually have a special salad and dessert menu for the exhibition.
Also, plan to sit in the back garden for a little while and read or listen to your iPod or whatever: delightful.
And if that wasn't enough for you--and I admit, it probably would be for me, but you could be tempted to travel to the 7th arrondissement and see a couple more exhibitions there.
Manet: The Man who Invented Modern Art at the Musee d'Orsay. Manet doesn't get enough credit, but if you read Ross King's book The Judgment of Paris you would know how very, very important Manet was to the emerging oImpressionist art and the modern styles that followed that. A colorful character, Manet also seemed to be a bit of a continuing pain... which might be the reason he was less successful, for example, than Monet. But the museum's website suggests that this retrospective puts Manet into historical perspective (like the King book) and shows the many influences on him, as well as his influence on contemporary and future painters and critics.
And I do recommend King's book as preparatory reading, if you are going to Paris because you want to see the art of the mid- to late 19th-century and the early 20th century, and really appreciate it in context. King is a fine writer and weaves his story beautifully, if with a few too many words.
Or you might head to the American Library and see their exhibition on Les Cafes Parisien, not very far from the d'Orsay. This set of photos by Anne Boudard captures the contemporary life of the cafes in 2011.
And for those of you who like antiques but don't want to travel to les puces, in the 6th arr. there is an antiques fair this June at Place St. Sulpice. Which gives the added benefit of putting you right where you can visit that church and see Delacroix's great painting for them, as well as one of the sites for Angels & Demons (ok, I don't care, but lots do).