Burlington VT is a great small city, as is Portland ME. Both are places I love to visit, with good brewpubs. Bennington VT has the Hennings Motor car museum and while I've not riden it, VT 100 is reported to be a great road to travel.
The state museum in Hartford CT has a large collection of Colt firearms, if your interested. My wife isn't into firearms but found the display fascinating.
Newport RI has the mansions of the rich and famous that you can tour, along with the International Tennis Hall of Fame.
MA has Plymouth Plantations (south of Boston), Boston itself (too much to list besides Old Ironsides in Charlestown), Lexington and Concord. The western part of the state is cool too. I believe the Norman Rockwell museum is in Stockbridge MA.
Funny, I live in NH and am not sure what to recommend here, other than perhaps the cog railway on Mt Washington. Not sure if it's operating right now. The Kangamaugas Highway is a fun road, as are most of the back roads up here. You can literally drive through all 6 New England states in a day if you want to push, but you wouldn't see much if you did.
Just some quick thoughts.
Jeff