I highly recommend Relais du Louve. The hotel was beautiful and in an incredibly convenient area--it was on a quiet street but just around the corner from everything--the seine, louve, shopping, etc. The staff was superb.
If you are a tourist--particularly if short on time--I recommend booking the "Big Bus" tour. There is a stop for the bus just 2 blocks away which was nice.
The next time I visit Paris, I will stay here without question.