I love the Musee D'Orsay, the Picasso Museum and the Rodin Museum. The Eiffel Tower is great but I didnt go up it and preferred to cross over to the Trocadero to take my pictures of it.
The queues for the Louvre were too off-putting and I was perfectly happy with my choices of museums that I did go to. about 6 years ago
To the above I'd add a visit to the Basilique du Sacré-Cœur, and then the surrounding Montmartre area for some decent food.
If you fancy something a little quirky I had a great time on a guided tour of Paris in a 2CV: http://www.4roues-sous-1parapluie.com/ about 6 years ago
My "must see" places in Paris are:
Notre Dame Cathedral,& walk around it to see the flying buttresses
Saint Chappelle for the amazing stained glass winows
There is a Monet exibition at the Grand Palais probably wort booking to avoid queues
Museum de Orsay is excellent
For an excellent panorama go to the top of the skyscraper near at Montparnesse Station about 6 years ago
Montmatre area is beautiful (including Sacre Coeur) I will also recommend to go to Pere Lachaise cemetery (you can take the Metro in front on Moulin Rouge, in the same Montmatre area) It is more like a beautiful and peaceful park than a cemetery, and you can find famous names such as Jim Morrison, Oscar Wilde, Edith Piaf, Abelard and Eloise, many artists and writers. It is full of ancient trees. A very nice please to sit down and see people passing by. It is also nice to take pictures! about 6 years ago