Here is a link to a map which shows "dark sky" locations, which combined with a topo map, should be useful for finding good viewing spots:
http://www.jshine.net/astronomy/dark_sky/
And another:
http://darksitefinder.com/maps/unitedstates-15color.html
Berkshire East Ski area is probably in one of the darker parts of Massachusetts, and it has a large treeless parking lot that has a good view to the north.
In southern Vermont, check out the Green Mountain National Forest off Route 9 west of Brattleboro in the vicinity of the Deerfield River. About 5 or 6 miles west of Wilmington, turn right onto Forest Road 71, follow for 12-13 miles and turn right onto Somerset Road, and follow for a few more miles until you get to the Somerset Reservoir. There is plenty of parking and a great view to the north across the reservoir. Or, follow Forest Road 71 north and look of clearings. It's mostly wooded, but it promises to be very dark and there are some marshy clearings along it's length, including one at it's northerly terminus with Kelly Stand Road. Primitive camping is permitted along Forest Road 71.
