I am going to Paris next month and I was wondering if anyone knew of any great sites I should see.?

I am getting married next month and we are going to Paris on our honeymoon. Of course Paris has the Eiffel Tower but what else is there that is a must see. I know this is a once in a life time opportunity so I don't want to miss out on anything spectacular. We will only be there for four days so a list of any landmarks/ museums/etc. would be wonderful!