Basing yourself in Boston or Cambridge is a good way to get to know eastern Massachusetts while not limiting yourself to one destination. On this itinerary, you'll get a taste of Boston and Cambridge, then set out on day trips to the history-rich suburbs. You'll go in roughly chronological order: Start in Plymouth with the Pilgrims; move on to Lexington and Concord to learn about the rebellious colonists; and finally, visit the North Shore, which flourished after the Revolution. If you're renting a car, note that you don't need it for the full week -- pick it up on (and don't start paying for it until) Day 4.
Days 1 & 2: Boston
Begin exploring downtown Boston by walking at least part of the 2.5-mile Freedom Trail. The whole shebang can be an all-day affair, but I suggest concentrating on the first two-thirds of the trail, from Boston Common through Faneuil Hall. Break for lunch at Faneuil Hall Marketplace, then head into the North End for a stroll on the main drag, Hanover Street, and a visit to the Paul Revere House, one of my favorite Boston attractions. From there it's an easy walk to Long Wharf or Rowes Wharf, where you can take a sightseeing cruise or, if you want to save both time and money, a ferry ride to the Charlestown Navy Yard and back. Have dinner at the Legal Sea Foods on Long Wharf, or return to the North End for Italian food.
On Day 2, prearrange tickets for a Boston Duck Tour, ideally one that leaves from the Prudential Center in the early afternoon. Be at the Museum of Fine Arts when it opens; consider taking a tour to give you an overview before you explore on your own. Head to the Back Bay for lunch and your Duck Tour, then make a beeline for the retail delights of Newbury Street. Newbury dead-ends at the Public Garden, where you can unwind and perhaps go for a spin on a Swan Boat. For dinner, check out Boston's take on French cuisine at Brasserie Jo or La Voile.
Day 3: Cambridge
Start in Harvard Square with a student-led or self-guided tour of the main Harvard campus. Up next are the treasures of the university's art museums, currently assembled under one roof at the Sackler Museum as the other two undergo extensive renovations; you may prefer the natural history museums, especially if children are along. Then head to lovely Brattle Street and the Longfellow National Historic Site. From there, walk along Mass. Ave. toward Porter Square, a route with some excellent shopping opportunities. In fact, this whole day represents a fantastic chance to mix shopping and snacking with sightseeing. Have dinner at Mr. Bartley's Burger Cottage, then hit a bookstore or two.
Day 4: Plymouth
Spend a day with the Pilgrims. Start with a 17th-century reality check at Plimoth Plantation, which opens at 9am. The hands-on activities are almost as much fun as mingling with the "settlers," who stay in character as they chat with visitors. In downtown Plymouth, have lunch at the Lobster Hut, where the deck overlooks the harbor, then explore a bit, starting at Plymouth Rock. Take in some historic attractions -- the Mayflower II is next to the Rock, and the Pilgrim Hall Museum is nearby -- before returning to Boston or Cambridge for dinner.
Day 5: Lexington & Concord
Spend most of the morning in Lexington, acquainting yourself with the earliest events of the Revolutionary War and visiting the historic Buckman Tavern. Have an early lunch in Concord and explore the beautiful town, picking and choosing the destinations and events that particularly interest you. I suggest starting with the Concord Museum, touring Orchard House, and stopping at Walden Pond on the way back into town, perhaps for a picnic dinner.
Day 6: Boston & Cambridge
After 2 days on the road, stick close to "home." Head to Dorchester and the John F. Kennedy Library and Museum, which is accessible by public transit and offers free parking (you're paying for that rental car, so you might as well get some use out of it). Spend the afternoon at the Museum of Science, allowing enough time for an IMAX film, if that appeals to you.
Day 7: Marblehead & Salem
Begin your day on the picturesque streets of Old Town Marblehead, a top destination for both sightseeing and shopping. If your hotel room rate doesn't include breakfast, arrive hungry and make a dent in a stack of pancakes at the Driftwood Restaurant. The Jeremiah Lee Mansion is a must if you enjoy house tours. Spend the afternoon in Salem, where the can't-miss destination is the Peabody Essex Museum; if time allows, also visit the Salem Witch Museum. This itinerary leaves you in a handy location for returning to Boston or for heading out to explore the wonders of northern New England.