If you're visiting Boston, go to the North End and find Salem street and squeeze into Neptune's for the best lobster roll in the city! They steam a chick lobster (one under 1 1/4 pounds) and break it down for you into a toasted roll--you can get it hot or cold--with mayo or butter--with a side of perfectly cooked handcut frites. They have THE COLDEST BEER in Boston and a huge array of oysters and other raw bar goodies. Seriously, some Winterpoint oysters, a warm lobster roll and an ice cold Newcastle with some crisp, salty fries is a great intro to New England!
http://neptuneoyster.com/by the way--I don't work there! I just love it!