I'm an American, but I feel compelled to throw in my personal opinions about Paris.
Paris is one of my favorite cities, though I've only been there once. Everything about it is gorgeous. The Lourve is, I think, a very necessary stop, though you'll never see all of it in one stop, even if you do it at a run. Best to work out beforehand what you want to see.
I'd also recommend setting aside a part of a day for just wandering around, taking it all in. A good starting place is in front of Notre Dame. It's been a couple years, but as I recall, from there, you can find your way down all manner of quirky little French streets with cute little cafes and interesting little shops. I didn't see any need to go for the very best in fancy dining--most places I ate at were cafes or bakeries that we happened by on the way. I like my travel loosely-planned.
The first food I had in France was in a little bakery within walking distance of Notre Dame. I ordered crepes and they were absolutely unforgettable, even if I had a hard time communicating what it was that I was ordering, since I had very little familiarity with French, and the cook spoke only a few words of English, and my accent was atrocious.
If you want to go somewhere that's a little off the beaten path (in other words, while it's a place a lot of tourists visit, it isn't the Lourve, Notre Dame, the Eiffel Tower, etc...though those are all well and good in their own right), I'd actually recommend the Catacombs. I wasn't too sure about them, but the friends I was with really, really wanted to go, and I didn't want to go off by myself so I tagged along. I was very pleasantly surprised. The atmosphere was very quiet, even peaceful, and it was a fascinating trip, and not even in a morbid sort of way. I think I may have wound up enjoying it the most out of our group, even. I've never seen anything like it in my life, before or since. Might be an appropriate place for a Downer to visit.
However, having my bag checked at the exit was probably one of the most bizarre things that happened to me--who would want to steal a bunch of old bones?! Be warned that there are a LOT of stairs, and if you're not up for some climbing, you might want to skip it.
I fell in love with a bar/restaraunt/pub (?--I'm not sure of its American equivalent) on a corner somewhere near the Catacombs. My friends and I went in during a slow time, and the owner was very, very friendly and outgoing and helpful. He even helped us try to learn French (a daunting task!), told us which subway to take to get to Napoleon's tomb, etc. The food was inexpensive but tasty, and I unfortunately did not save either the business card of the place, or the reciept so I'm afraid I can't tell you its exact name. I believe it might have been also within walking distance (or even across the way from) a McDonald's. It wasn't fancy dining, or even a place that looked particularly geared towards tourists, but it was lovely all the same.
I'm going to go home for veteran's day weekend, the weekend after next, and I'll try to find you the business card from the other restaraunt I really liked in Paris. I believe I saved it. They served couscous, of all things, and it was a very interesting taste experience, though I have no idea of its price range.
A word of advice--When walking into any of the many stores in France, do say "Bonjour", and when leaving, say "Au revoir". It's a custom, or so I was told in school before going. Not to do so would be rude, apparantly.
Aside to Bethberry: I wanted to go to Parc Asterix, but didn't have the time or the transportation to do so (I went with a school group so our time was more structured than I would have liked). Glad to hear it's a good time. Perhaps I'll check it out if I'm fortunate enough to go to Paris again.
I can apparantly ramble on for ages about Paris, but really. Even if you go in with hardly anything planned, you won't find a shortage of things to see and do, on the spur of the moment. A day spent wandering the streets is not, in my opinion, a day even remotely wasted.
EDIT: Just saw Mithalwen's post about Creperie des Arts. It sounds familiar, and if that's the place I'm thinking it is (I barely remember--Paris was a whirlwind), then I heartily second the recommendation!