D'Orsay, Centre Georges Pompidou, obviously the Louvre.

Sainte Chapelle is high on my list.

Eat lots. The food is awesome. Interact with people less. The food in Paris is awesome, the people aren't.

Whatever you do, attempt to do get there before the Asian tour buses do. This typically means get to your destination before 11 am and most times, 10 am. You'll be able to move more freely and get closer to things you want to see if you get there before they do. They move in groups, and once all the groups are there, they (the groups) move independently of one another. This basically means you have groups of about 70 people at everything you want to see, at all times. Luckily, they only stop at major tourist attractions. So, schedule your visits to major things early in the morning, then go to smaller places later on in the day.