Being from New England there is so much I want to tell you to see. Newport, RI is gorgeous, you can tour the mansions of the obscenely rich and famous. September is a good time of year too, after the tourist season. Providence RI aslo has great theater shows and a neat down town area. In Massachusetts, of course there is Cape Cod and the islands of Martha's Vineyard and Nantucket. Great B&B's on the islands, but you need to take a ferry to get there. There is also the historic town of Plymouth, the Pilgrims, etc. Boston is great also, but traffic is a nightmare because of the Big Dig, and parking is a major problem in the city. Further on up the coast is Portsmouth, NH, a very quaint and picturesque town, neat shops, beautiful scenery. Now on to Maine and where I grew up. The whole coast is gorgeous and worth seeing if you make it that far. York, Kennebunkport, Portland-very neat downtown area called the Old Port, Boothbay, Bar Harbor, Rockland all so beautiful with plenty to do and see. Portland is about 2 hours north of Boston if you're trying to plan your time. There is also a the Sebago Lake area (where I grew up) just west of Portland. It's about 2 1/2 hours from Boston.
I hope you make it as far as New England. September is a perfect time here, the summer tourists will be gone, but the weather will be beautiful. Good luck and hope you have a great time.