Well July means heat, so my thoughts go northward, not south to higher temps--but I know people have different feelings about the heat.
Virgina/DC/Maryland area is so full of stuff to see and do. I spent a week in Winchester, VA visiting WV, Shenandoah Valley & D.C. I would have liked 2-3 weeks in the region.
Acadia was one of the first to come to mind.
St. Lawrence River (Heart Island/Alexandria Bay), Finger Lakes was another.
Lake Champlain regions (NY/Vermont), Audible Chasm.
I'm sure you've done Niagara, but you could consider the Canadian side's Provincial/National parks or the cities of Toronto, Ottawa, Montreal, Quebec
For a more unusual choice... I'd say Nova Scotia. Supposed to be a beautiful rugged country, reminiscent of Ireland. Very Friendly people (Newfoundland is very expensive to ferry to, skip it). But I think that would be more of a 14 hour drive from Hartford+customs.