Stay off the interstates and drive via state roads, and you'll see a lot. I've lived in the Northeast most of my life, and always found the best foliage in Vermont, with New Hampshire a close second. There are lots of great places in upstate New York, Western Mass, and Pennsylvania Dutch country, too. Stick to the higher elevations and valley views for the best viewing. Take your time, spend a day in a few small towns, and you'll have a good experience.
Let's say you start somewhere near Portland or Augusta. Head West to Montpelier and then on to Burlington. Spend a day in Burlington. Follow Rt 7 down to Rutland, then you can decide to head West into Saratoga Springs, NY and West on 29 into the Adirondacks. Or keep going South into Stockbridge, MA. Stockbridge is a great, little town. Say hello to Arlo Guthrie and visit his farm if you're a fan. If you're a foodie, keep going South from Stockbridge into Great Barrington. Spend a day or two at either or both of these towns.
Head West into upstate NY. Hudson, NY is a hipster paradise with tons of fun things to do
http://gotohudson.net/, walk along Warren St and browse antiques, laugh at the celebrities in town, enjoy a book and a beer at the Spotty Dog Books. See a show at the Basilica or Club Helsinki, or if the timing is right the Hudson Opera House. Have lunch at Bruno's, run by a good friend of mine and her sister. They make everything from scratch daily using mostly local ingredients.
From Hudson take I-84 West, then pick up Rt 209 at Milford. Drive south through the state forest and through the Del Water Gap. Head into Stroudsburg, PA and make your way West along the mountain routes with great views of the valleys. Optionally take Rt 81 south into Hershey and spend the day at the park or enjoy a car show on the weekend.
From there you can head West on I-76 and into Maryland, Virginia and West Virginia. Skyline Drive in Virginia is gorgeous and runs for hours along the mountains, worth a day or two in the park for sure. You're on your own from there. Hope this gets you a few interesting routes, sounds like a fun plan!