Paris is justifiably fantastic. If you're going in the summer, during peak season, I'd expect few deals. In addition to all the sights, one don't-miss IMO is Berthillon ice cream on the Ile St. Louis. Quite possibly the most perfect ice cream anywhere. Also, eat as many pastries, baguettes and stinky cheeses as you can get your mitts on.
My advice? Try not to stick out like an American tourist. Our reputation as a people is, unfortunately, justifiably deserved (especially in Paris, where there will be hordes).
One thing that will put you leagues ahead of your fellow countrymen? Greet, thank and say goodbye to all shopkeepers, even if you aren't buying anything, and do it in French. Also learn "désolé, je ne parlais pas français, parlez-vous anglais?" They don't expect you to speak French, but they also don't expect you to assume they speak English. This one phrase, which acknowledges the fact that you don't speak French, will put you in good stead with almost anyone you meet/encounter.