New England

None until you get to Maine.

Boothbay Harbor is nice. Just seems as if the entire state of Maine is covered in lobster pots though!

They have to catch them if you're going to eat them. Bar Harbor is nice too, but that's in Maine. Several nice spots there, beautiful scenery all along the coast, but it's rugged. Most spots between Boston and Maine are fishing villages like Glouchester. Big swells are common. My one time up there we stopped near Portsmith, N.H. Nice dock, but we were a car ride away from town.
Now you could easily spend a week or two exploring places between Boston, Newport, the Cape, Vinyard and Nantauket. I'd do my touring down there before heading up to Maine.

Newport, R I. Spectacular mansions, quaint architecture, good harbor, etc.

What do you like?
How big is the boat?
I like Marblehead/ Salem. Both are nice little towns for walking around.
Head into Gloucester and go up the Annisquam River, and pop out on the north side of Cape Ann. Spend the overnight in Newburyport.
Next stop is Portsmouth, NH.
Nice town with good facilities.
Now you are in Maine.
Portland is a great city, marinas right downtown near all the action.
North of that it is small harbors, gunkholing, etc.
Now it really comes down to what your likes are.

I have spend years in these waters and here are my thoughts:

Newport, RI- The sailing capital of the US if not the world. Great places to eat. Nice town. Good marinas.

Block Island, RI- cool little island with its own feel. Hard to get a slip or a mooring during the summer, but the harbor is pretty protected so anchoring is not a problem (actually most of the boats anchor).

Marthas Vineyard- many places to stay... have not spent much time there. Vineyard Haven was nice, especially on the 4th as you could see fireworks all up the coast of the cape. Vineyard haven is pretty quiet. Cool "lake" to explore by dinghy.

Nantucket- Personal favorite. Upscale. The best dining of any of these places. Very COOL Marina with lots happening. Great town, and great beaches!

Boston- out of the way if you are headed to maine

Maine: they are not lieing when they say there are thousands of pots. It almost makes running a sport fish like ours impossible. Just leave yourself extra time if you have a fast boat as you won't be going fast. Pack a wetsuit.

Southwest harbor- nice quiet harbor with a nice marina. Great town with oddly amazing food. Not a tourist trap like bar harbor and there are free busses to northwest harbor and bar harbor.

Camden- nice and small- the harbor is just picture perfect. a nice contrast from Bar/NW/SW harbors

Actually, the bottom in the Great Salt Pond is very silty. I'd call it's holding as poor. (I nearly disconnected the electric to the island a few years back on July 4th weekend when I dragged anchor with a 60' Sunseeker). Better to get a mooring. Plus Andiamo cruises the anchorage with crousants in the AM. Dockage and moorings aren't hard to get last year or this. Call a couple days in advance for a res. for weekends. Mid-week, no problem. Old Harbor is mor of a day anchorage, and gets crowded. It's in the heart of tthe town. Watch the tide there.

Don't forget to BYOB to the restaurant for dinner. V.H. is dry. Really! Personally, I prefer Oak Bluffs as it's in the heart of everything and just a bike ride to Edgartown or V.H. SInce the island is one big traffic jam bikes are a good way to go. O.B. has lots of restaurants, a carosel, beaches, great picturesque "cottages", but it's also got the ferries and crowds.