Well, I Loved the Beaches of Normandy and Mt. St. Michel, which are pretty close to each other I believe. There's Paris, of course, and I've heard really great things about Arles.
Etretat in Normandie, Le Mont Saint Michel, Castles in Loire Valley (Chambord, Chenonceau etc...), Paris definitely
I loved the wine route through Alsace. Very quaint, picturesque little villages (as well as some great cities...Colmar and Strasbourg)
The Catacombs and Pere Lachaise in Paris, the Normandy beaches, and the Iles Frioules near Marseille. Although Aix is lovely, too.
No mention yet of St Malo, so let mine be the first!
I would have to second some of the others posts...Mont St. Michel and the Normandy D-Day beaches are awesome. Both can be done the same day. Paris is of course a must stop as well, and there is plenty to see and do (the Catacombes are amazing!)
I would second Arles also...and probably double it up with a stop in Avignon. Both very interesting.
The Loire Valley, esp Chenonceaux and Chambord.
Bottom line is there are plenty of places to stop and see! Depends on your interests really...
At the other end of the country I should mention Antibes, where I would own a villa - in my dreams.
Laon, Avalon, Montpellier & Arette
You have to get to the south!
West to East
Biarritz - Great surf town...loads of nice beachs
St Mont - Little village off the track eastwards - VERY good wine at Plaimont (www.plaimont.com) and Chateau de Sabazan is worth a stop . Also excellent tiny b&b called Chateau de Projan (www.chateau-de-projan.com). Home made food for dindin!
Carcassonne - Medieval City - take the tour around, it's worth it - Ancient hotel in the center called Hotel de La Cite (www.hoteldelacite.com) with a little wine tasting room next door (can't remember the name but literally next door)
Montepellier - any city that still has Roman aqueducts standing, will always be cool in my book