What to do around Paris?

I don't think there is really such a think as a "must do" bit o can give you some ideas of places I have enjoyed.
Chantilly - Royal stables and the Chateau houses an incredible museum.
Pierrefonds- lovely lakeside setting,best done by car.
Provins - world heritage site, medieval ramparts,and some good shows(Birds of Prey ,jousting etc)
Rouen- only 1.5 hours from Paris, half timbered houses in old section .
Loire valley- take two three days touring chateaus and tasting wine!

The chateaux of Vaux le Vicomte is beautiful and less crowded than many. Check their website. If you can visit on one of the candle-lit evenings, do it... I'm not sure if those extend into the fall.

A night or two in Colmar would be enjoyable. You could stop in Strasburg on the way.

If you haven't been to S Denis, it's a beautiful example of very early Gothic. Also, the cathedrals at Reims, Amiens, etc.

Chateau Malmaison, a 15 minute bus ride from La Defense.
Parc Butte de Chaumont and
Chateau de Vincennes (both in Paris)
Inst du Monde Arabe , also in Paris
Promenade Plantee, just behind the Opera Bastille

If you want to go further afield and don't mind the TGV prices (or can book far enough ahead to get discounts), a day or two in Lyon, Nancy, and/or Strasbourg is very worthwhile. Nancy and Strasbourg combine very well as a two-day trip, since they're in the same direction (Day 1: Paris to Strasbourg; see Strasbourg, sleep in Strasbourg. Day 2: Strasbourg to Nancy, see Nancy, late train back to Paris). If you go to Strasbourg, don't miss the Museum of Alsatian Life. Nancy is a must if you're interested in Art Nouveau or glassware. And Lyon is my favorite city in France outside of Paris.

I'll put in another plug for a quirky Paris sight: the Museum of Counterfeits, near the Porte Dauphine Metro. They not only have fake designer purses, but more sinister things like fake medicines and fake car parts that have caused fatalities. And the Porte Dauphine station is a sight in itself, as it's one of the most intact station entrances, with all the original features that have been stripped away from most others.

Fontainebleau, Giverny and Vaux-le-Vicomte (as Sherry already said) are top of my list.

In Paris, I highly recommend the Nissim de Camondo museum next to Parc Monceau, once the home of a wealthy family.

Chartres, Reims, Bayeux not mentioned so far on this thread. Chartres is the easiest, about an hour on frequent trains from Gare Montparnasse. The others take longer and/or cost more. I agree with the poster who suggested some overnight trips if you have a whole month.

Ina Caro's Paris to the Past describes 24 historic and beautiful places she's visited, either in Paris or (except for one) a day trip by train. She tells you what train to take and often recommends places to eat. The history is fascinating and descriptions evocative. The link is to the Amazon description, but you could look for the book in your library and use it to help you choose places to visit.

I wouldn't presume to speak for all the Francophiles on this board, but, a month in Paris, wow!

One must see sight in Paris is the Saint Denis cathedral. It is often over looked because of Notre Dame but Saint Denis was one (if not the first) gothic cathedrals in Europe. In addition, most of the kings and queens of France, along with Saint Denis himself are burried in the crypt which you can visit. This was one of my favorite places to visit.

I highly recommend the Michelin green guide to Paris and the guide to the area just outside Paris. (In French it's Environs" but I'm sure it's translated into English. Very informative. We used those for years.

There are dozens of trips within an hour of Paris by train. You can see some of those in my photo journal
http://janettravels.wordpress.com/category/day-trips-from-paris/

These are just a few of the more recent ones we have done. Other great trips include Fontainebleau, Auvers sur Oise, Chantilly, Ecouen, even a train to Tours where you can get a day tour by van of nearby chateaux.

Get Simms book 'An Hour from Paris' She gives directions for 20 such trips some of which are in my journal. She doesn't do the obvious ones like Giverny, Versailles, Chartres etc but less well known spots to the average tourist like Moret sur Loing or Crecy la Chapelle.

If you haven't done walking tours of the arrondissement or walked the Promenade Plantee or spend a day in the Bois de Bologne, get a couple of good 'walking tours' type books and do some of those. We have spent months in Paris and are still finding spots we haven't visited. You can see some of our Paris walks in the Photo journal as well -- just choose 'Paris' as a category on the side of the page.

Thank You! Thank you! Thank you This is exactly what I was looking for! Everything has been so helpful. We've already ordered several books and checked out the new websites. Perfect!

Lots of good ideas above. I've always had a soft spot for the Institut du Monde Arabe. Auvers-sur-Oise is covered in Rick's Paris book, was popular with many painters, and is where Van Gogh shot himself an is buried. Someday, I'll try the canal boat ride by www.canauxrama.com from Place de la Bastille to La Villette; in that neighborhood, I believe Marc Bittman of the NYT likes the traditional restaurant Au Boef Courronne.

The Pierre Lachaise Cemetery is interesting. It's hard to find some of the famous folk there - I got a small map at the entrance but it listed the many famous, and not-so-famous folk, numbered in alphabetical order. I thought the holocaust section was particularly moving. Rent bikes and spend a day in the Bois De Boulogne.

Mini France was charming. There are miniatures of all the famous sites in France with very good landscaping. It's easily accessible by bus. A day trip to Reims has been on my list for a while now - cathedral plus champagne houses (you need to make reservations in advance).

Don't miss the Journees du Patrimoine in Paris - should be the 3rd weekend in September. Most of the local and state government offices are open to the public - the only time they are. Some of the embassies also open their doors. The lines can be long, but it is well worth the wait to see the palaces and mansions of Paris that house them.

In Paris, I enjoyed both the Cluny and L'Orangerie museums. A day trip/overnight to Brussels is doable. We did a three night side trip to Brussels and had a great time there.

Also note that the Paris Museum Pass is also valid for many of the chateaux and museums in the region, even if they're quite far outside the city. Check the list on the website.