Don't normally post but lived in Philadelphia for two years so:
Near (relatively) to Boston - Cape Cod for food, drink and whale watching
Niagara definitely within reach and worthwhile.
Maine - wild and beautifully empty.
New Hampshire / Vermont - not so wild but beautiful, particularly Stowe / Burlington / Lake Champlain
New York State - stunning, although we were there in Autumn
New York City - as above, unmissable
Philadelphia - Liberty Bell / Benjamin Franklin / scenes from the film Rocky. Plenty of history including battle sites from the War of Independence. Amish country in Lancaster county an hour east of downtown.
Washington DC - as above, has to be seen particularly the area around the Potomac River. - Lincoln Memorial, Cenotaph, White House, Korean War Memorial.
Two weeks wouldn't be enough
One point though, if you can drive really worth renting a car.