In addition to flying, there's also Eurostar train service and, if money is an issue, Eurolines overnight bus service (which I will get to experince for the first time this coming weekend...).

There are several threads on "must-do's" in Paris in the Paris forum, but the obvious ones like the Louvre, Musee d'Orsay, Eiffel Tower, etc. come to mind.

Enjoy!

Alex