We love museums and art, but not for all day, or day after day. We were hoping to go to the various museums and see the most famous paintings (Monet, Renoir, etc.) and then just add more as we want. Will these painting be scattered around the museums or will each artist have it's own area? Just wondering how likely it will be that we can focus on those artists and not spend time on the less known ones (or at least less known to us)
The Louvre is fairly consistent in having art classified in eras and styles, ex. 16th century Flemish, 15th century Florentine, etc. Within that, they keep the artists pretty much together, but not absolutely. In the Orsay, which is mid 19th century to early 20th, they will stay closer to individual artists, since the styles are pretty much pre-impressionist, impressionist, and post-impressionist.
Check out the Pinacotheque de Paris on the north end of Place Madelaine. They have rotating shows of collections of single artitists and family's of artists at 3 separate galleries in the neighborhood. Since they are a private museum, they are not part of the museum pass. But see what is showing when you are there, and stop in if something trips your trigger. http://www.pinacotheque.com/en.html
The Orangerie is by artist. I was able to get up behind Montmartre and find exactly the location of one of the paintings within an hour.
Marmatton -- amazing Monet rooms, and you can skip the other floors if you choose. Rodin museum and garden.
There's a Delacroix museum and a Picasso museum (may still be closed).
An advantage of the Museum Pass is letting you pop in and out museums to see a few pieces without feeling like you're wasting an admission charge. Go to the Louvre or Orsay for one artist or period, then leave, then go back next day for another, etc. You don't get "museumed out," at least not right away, and you skip the lines (except security). That said, Orsay, Louvre, and Pompidou are the only ones I can think of now that are overwhelmingly large and tiring (maybe Branly too, I haven't been). The others are small enough to do justice to in maybe a couple of hours.
At the Musée d'Orsay, you'll find the grand collection of Impressionists up on the top (5th) floor. A good strategy is to make a beeline for the back left side of the museum upon entry and then take the sequence of escalators up to the 5th floor; you then walk forward through the Impressionists.
Rick gives a great sequence for getting through the Louvre and conserving your energy and time for the "greatest hits"; I'm sure it's available as a podcast or walking tour on this site (he has the same thing for the Orsay, but I don't know if it's been updated since the galleries were rearranged a couple of years ago).
As Sam said, the Louvre sorta keeps artists together...but they do have special exhibition rooms like their Grand Canvas rooms, etc. , with all large-scale paintings grouped together.
You can also go to their website and do a virtual tour of the museum, so you can plan your attack. Definitely get the Museum Pass!
My greatest joy has come from thinking I wanted to see 'The Famous Ones', then learning that I actually fell in love with works I'd never heard of before :-) Do allow yourselves plenty of time for just wandering and finding new passions!
Also, if there is a specific piece that you are going to see, make sure it's there. The "Mona Lisa" doesn't move, but some of the other ones do. We went looking for one of the pieces mentioned in RS book, only to find it was out on tour.