The Arc de Triomphe is exactly what you see: an arch in the middle of a 7 lane roundabout. In case you are trying to count the lanes to make sure I am right, you can't. You read that right. It's a seven lane unmarked roundabout. You can get next to this arch by taking the underground passage way. And there is a fee to come above ground again. There is a neat little feature that this monument offers. You can climb to the top of the arch and get a nice view of the city.
The Norte Dame Cathedral is a must see. I find this Gothic styled church to be so charming. From the gargoyles guarding the outside to the awesome arches inside, this church has an atmosphere that goes unmatched in the rest of the city. There is a treasury in one of the wings of the cathedral. If you have time I suggest going though it, but if your on a schedule don't worry about missing it. Simply being inside of the amazing structure is enough of an attraction.
The Louvre. What can I say that you don't already know? Its a great museum that would take days to fully explore. There are extremely well known pieces of art in here. And for those of you that don't know a thing about art, have no worries. This place is, simply put, amazing. And as far as the Mona Lisa goes, yeah, she lives here, but she isn't as big as you might think. For as enormous you see this building being, you might be surprised to find out that it actually has many underground levels that make this place much bigger than it looks. You are allowed to take personal pictures of the permanent exhibits. Another good to know fact is that if you are traveling with a stroller, there is a special entrance that has an elevator. I use the word special not because it has an elevator but because this line is usually much MUCH shorter than the normal entrance line. Once you get lowered into the reception hall, check your stroller if you can. This place is not easily accessible for them. However, it can be done.
The Eifel Tower, like the Arch de Triomphe, is exactly how you picture it. Its a neat thing to see, but it really isn't any different than the pictures you see. There is the option to going to the different floors but there is a fee. In my opinion, I think that it is best to admire from a far. The pictures are better, too.
The palace of versailles is such an influential building. Not only have many extremely important people walk through these halls, many building have been built based on its achritetural design. I was blown away by the attention to detail this palace represents. Not a single thing was over looked during the assembling of this place. The hall of mirrors left me standing in awe.
The only suggestion I have for visiting is if you can avoid "high season/times", DO! It can get very crowded and hard to get to maneuver. Pictures are allowed to be taken inside.