Hi Denise,
I am a northern Californian living in the UK, and my do not miss recommendation for you is Provins. Think a medieval version of Virginia City. It has 43 structures built in the 13th century, and has living history exhibits such as falconry displays, middle age siege weapons demonstrations, and an awesome medieval horseback riding show. It is a do not miss for people from the new world.
An hour North of DLP is Compiegne, where Napolean's favorite home was (as well as where Joan of Arc was captured), or Pierrefonds, a lovely storybook town that looks right out of the 3 Muskateers, with a great castle, and of course the railway carriage where the armistace for WW1 was signed is between the two towns.
About 80 minutes to the east is Rhiems. Now, most English speaking people are unaware that the Notre Dame here is historically more important than the one in Paris, as it is where all the medieval kings of France were coronated. Also, there are several champagne wineries to visit. Now I know Napa Valley and Sonoma have similar offerings, but the Tattinger Winery is in the cellars of a 13th century monestary (so a little different).
Also, Vaux le Vicompte is worth visiting on a Saturday night, it is only a little way from DLP and it was the mansion that inspired the sun king to build Versailles. In fact, he was so jealous, he imprisoned the owner the day after the inaugural party, and the official that built the chateau died in prison. On Saturday nights, they line the gardens with candles.
The other really great place to check out is Chantilly, about an hour north of DLP. It is a wonderful old town, but the chateau has the largest library in France after the Louvre, and contains the book Le Duc De Berry, the artwork that inspired Walt Disney's animators when designing the art direction for Sleeping Beauty (the castle looks like it belongs to Cinderella's step mother). The grounds also houses an equine (horse) museum, where there is an enormous mansion for horses (the owner thought he would be reincarnated as a horse), and as well as having lovely exhibits including a carousel horse display, it also has lipenzer stallion dressage and training displays. Also, Chantilly is reknowned for the sweet whip cream, very popular on waffles (guaffre) or ice cream.
Barbizon is nice if you like impressionism, it was an artist colony during the impressionist movements.
And DLP is in the Brie region, so the cheeses at local markets such as Meaux are great choices.
If you like war time history, La Cople, 3 hours north of DLP, is where all the V2 rockets were tested by the nazis, and near by is the Artois region town of Arras, where there are immense underground tunnels to explore, first built in the medieval age, but essential for the allied wins in WWI, also the town has beautiful unique architecture, especially the town hall. also, a huge Canadian War cemetary is 3 miles out.
5 hours to the North West of course the Normandy Beaches, Mont St Michel, and the Beayeux Tapestry (c1086) tells the story of the Norman Conquest of England.
4 hours to the North East, you could pay a visit to the WWI trenches or Brussels, the capital of Europe (with some great architecture again), or the beautiful medieval canal town of Brugges (with more canals than Venice).
Nearer to DLP, if you like coasters and shows, Parc Asterix is great fun. Think more 6 Flags Discovery Kingdom in Vallejo, but with better theming. Warning though, it is 100% in French, but my wife and kids do not speak French, but they still enjoy it.
Also, if you like shopping, Val de Europe is 2 miles from DLP, and it is one of the biggest malls in Europe, with a designer outlet, an Aquarium, and some great dining options.
we have been on vacation in the region over 50 times in the last 20 years and not seen it all. And as much as I love DLP, I really think people that just keep going to the parks are missing out on so much. There is far more to the region than just Disney and the city of Paris.