Visiting foodies need French restaurant rec
Depending on the size of your party and the kind of ambiance you'd like two excellent options are Bistrot Lepic and Bistro Bis (already mentioned). For a smaller group and cozy, relaxed vib, I'd recommend Bistrot Lepic. For a larger party, more upscale decor, and livelier atmostphere, Bistro Bis would be a good bet.
Marcel's is my top pick for French, as well. Although I am not sure how big your group would be, and it isn't a huge space, and is a little more intimate. They have an excellent menu that you can really customize, and they have an excellent wine list. The boudin blanc is light as air, the lobster bisque very good, I just can't think of a dish on their menu I have had that I didn't really like.
My Second and third choices would be:
Le Paradou, which has a very nice modern decor and creatively prepared modern, but classic french menu; and
Bistro Bis (be sure to get escargot they have great preparations, I love the red wine one) which is more of an upscale Bistro, but I think they have great food, that is rarely if ever disappointing.
You might search the board for a rather recent thread Best French, which I think has a good discussion of many of the best French restaurants in the city.