I went there years a go on a college trip, visiting art galleries. I was so broke though, I didn't see much. This time I hope to see a bit more (apart from the riots of course) like the Catacombs
http://www.ibiblio.org/wm/paris/cata/walls.html
the sewers
http://www.sewerhistory.org/grfx/wh_...aris_tour1.htm
Notre Dame and probably the Eiffel Tower although I've climbed up it before (cheaper than the lift!). Maybe a trip down the Seine at night, if there's not a curfew - see Paris lit up, including the mini Statue of Liberty.