Darner suggested some really good things to see and do, but don't try to do it by train. You'll really need a car. Most of these places aren't anywhere near a train station. Remember, the train system is designed to move people where they need to go on a day by day basis, not to the tourist areas. You can get to the major cities, but then you'd still need land transportation. (Versailles is an exception, a short walk from the train station there).
At Normandy, be sure to go down to the actual beach. There are paths from the Cemetery. Also don't forget the other beaches. We only really looked at Utah and Omaha. Somewhere, I forget where, there is still a rusted landing craft still sitting on the beach. Finally, drive on down a little further to Point du Hoc. The craters are still there from the Allied bombings and the German fortifications remains are there.
Definitely see Mont St. Michel. It's a long walk up but worth it. Be sure to take the tour at the top.
Go to Versailles for sure. You can do that by train or car. We also saw Napoleon's palace Fontebleu (sp?) which is also worth seeing. (Again, you'd need a car here)
Of course in Paris there's all kinds of stuff.
You'll need to check your maps and plan. Some of these will make pretty long day trips so be prepared.
At Disney, don't miss the Wild West Show. That would expecially fit in with your stay at Sequoia.
Have a great trip.
