Some of the most impressive things I've seen in Paris:
Sacre Coeur - Church of the Sacred Heart, a wonderfully exotic architecture for a Christian church on a hill in Montmarte
Notre Dame Cathedral - there aren't many free things to see in Paris: this is one of the few, and a definite must see!
La Defense - when you get tired of all the history and culture, hop in the metro and discover this oddity in the middle of financial district.
Louvre - not for the faint of heart. The anecdote goes: 'If you stop for 30 seconds to look at every picture at Louvre, you'll spend 2 years there'.
Quick Tips:
Tip about France:
Don't tip! :) (unless you really want to) It's included in the price.
Best Way To Get Around:
Three words:
METRO, METRO, METRO!