Well - of course the Eiffel Tower, Montmartre, Centre Pompidou, the Louvre, Arc d'Triomphe, Notre Dame, etc. Eat a lot of tasty foods - I love crepes personally and they come in lunch versions, but patisseries are another favorite stop of mine. Paris also has good Asian cuisine if you're into that. I'm a budget traveler so I usually drop by a bakery and get a coffee and some breads (the French know how to do this well) and me and my bf also have dropped by the big supermarkets to get some cheeses and bread to just eat in a park in the past. Also don't forget to go through the city at night time - I personally love Paris at night.
And be generally aware of potential pickpockets in touristy areas.
