Versailles is a short (<1 hr.) train ride from Paris, as is Chartres, which shouldn't be missed, not only for the Cathedral but for the quaint old streets and timbered buildings behind it. For train info, check out
sncf and
Rail Europe.
Oh stop it, this is driving me crazy! Mr. M and I have a Paris/London trip tentatively planned for October, but I'm starting to get antsy!
I wish we had gone out to Versailles and Chartres, but we just had so much to do, and with the crowds there at Easter (2 years ago it was) the lines just took up so much time for the museums etc. I've never seen so many people in one place! October sounds like a good time to go. Everybody is back in school, no bank holidays probably then, you should have no problem. Best to go at a time like that.
We were just limited by our daughter's school break so had to go when we could. We spent 4 or 5 days in Paris, then went down and spent about a week in the south, right on the water, near Antibes. That was the best part! The south! Not nearly as crowded, great food, the weather was beautiful, and it smells so wonderful in the hills there.