Musee D'orsay

Situated just across from Le Louvre, Musee D'orsay is worth visiting just for the architecture alone. It's a beautifully renovated train station, converted of course to be a museum. The art stored is mostly impressionist. If you are short on time, start at the top and move your way down. Unlike Le Louvre, the overall quality is consistently high and it's possible to see everything in a few hours.