Definitely have a look at A La Carte rental apartments if you're staying for more than a couple of days. We stayed at one of their rental residences, and loved it, feeling more like a local than staying at a hotel. Prices range from moderate to luxe. The advantages: immersing yourself in central Paris where all the monuments are, walking distance to everything, plus tips from A La Carte on how to make your stay better, great apartments and great people to deal with. They get my vote! We plan to stay with A La Carte again on our next trip.
BTW the rental apartments vary by area, we stayed in the Marais last year which is quite a trendy area with lots of shopping as well and within a 10 min walk of the Louvre. Next time we plan to stay in the Latin Quarter (the Left Bank). Once you've seen Paris, you can't get it out of your blood. (IMO - Two West Coast Canadians).