We'll be heading up to Boothbay Harbor in Maine this weekend from Boston to check out a railway museum there, as well.
I second the narrow gauge in Portland - there is a small museum and a ride on the rails available. When we were there 2 years ago, the conductor had just liquidated his O scale collection.
If you're near Kennebunk (port) in Maine and like seafood, be sure to check out The Clam Shack - their lobster is world famous - they catered at least one of the US/Russia summit meetings when G. Bush was President and lived in the area (he still does).
If in eastern Massachusetts near Boston, take a ride over to Charles Ro in Malden to check out their store.