If you like to go to museums, the Peabody Essex Museum in Salem is a really nice small museum. http://www.pem.org/visit/ They have a great section on all the sea going trades that shaped that area. And I second the Strawbery Banke suggestion in Portsmouth NH - actually, all of Portsmouth is a fun place to visit.

If you do find yourself driving up the coast from Salem MA to Portsmouth NH, stop by the Beach Plum ice cream stand on rt 1A in North Hampton NH. Yummy, yummy!