Depends on which route you take. If you are into Gambling, the casinos in Connecticut may be worth a visit. If you are into things military related, the Groton Sub base can be cool, as well as Mystic Seaport for the family fun thing. There's also an aquarium in Mystic, the mansions in Newport, and some nice beaches in Rhode Island.
If you take the inland route there's Sturbridge Village in Massachusetts.