Where would you suggest travelling in France for one month by car?

Brittany, Normandy, Champagne, Loire, Languedoc, Dordogne, Provence are all possibilities. I'd avoid Paris with a car. Also note that the train system is very good, so you could combine car and rail.

Get the Michelin Green Guide for France which will indicate the major attraction and map out an itinerary from that. Or concentrate on one or two areas and get the guides for that. If one or two areas, I would do Normandy/Brittany as one area, and then drive down to the Dordogne. On that drive, stop by a couple of chateaux in the Loire valley. Visit the abbey church in St. Savin (about 30 km. east of Poitiers) and visit Oradour-sur-Glane near Limoges.

I've used the Michelin Green Guides and they are really good.

We just returned from 3 1/2 weeks in France, and after we left Paris, we rented a car and went to Normandy,then Dordogne and Provence. The advantage of that much time is that you can avoid the autoroutes, take the smaller roads and see all the wonderful villages, architecture dating from several centuries and lots of things you won't get just driving the autoroute. I wrote about our trip in a trip report "Our Month in France - Paris, Normandy, Dordogne and Provence." Take your time and plan on a few stops and be willing to improvise once on the road. I second the stop at Oradour-sur-glane.

My inclination would be to visit Normandy and Brittany, then take the train to Dijon, pick up a car, do some sightseeing in Burgundy, then take the train south to Provence. This would give you some great highlights for future planning.