http://www.flickr.com/photos/professorbop/621653989 Brattleboro I quite liked living in this area, Brattleboro, VT. It's a tad small for your guideines (12,000), but it's part of a general area that includes Keene, NH: http://www.flickr.com/photos/the-dining-philosopher/78184680 Keene and Greenfield, MA. Brattleboro has a very artsy, old, industrial feel and a big art scene for a city its size. http://www.flickr.com/search/?q=Brattleboro&w=all
My hometown of Lincoln, RI was rated #60 in the 2007 Money mag poll of the top 100 places to live. Pretty much anywhere in RI is close to the cultural amenities of Boston and Providence (and Foxwoods Casino in CT). Lincoln has slots and computerized table games at Lincoln Downs (dog track), it's a very nice casino. Lincoln still has that quaint New England practice called the annual town meeting where they discuss the budget (and every crank and crackpot shows up, it's a delight! ) K
I visited Flagstaff but while the landscape is obviously beautiful, I wasn't very impressed with the town I have to say.
Ithaca is great if you don't mind 300 sunless days a year and a suicide rate somewhere above 30%. Here's an article from BizJournal about the best small towns in the country. Now, I've never been to Bozeman or Lexington Park, but I have been to Torrington. As a matter of fact, I was born and raised there - and I could never, ever ever recommend anyone move there. Which doesn't speak well of the places on Bizjournal's list that fell behind my hometown. If you want New England charm, go for Williamstown, Massachusetts or Keene, New Hampshire. Of all the small towns I've been in/through, my three favorites were Monterey, CA, Flagstaff, AZ and Frederick, MD. What's not mentioned on Frederick's wiki link is that it has an absolutely amazing brewpub right on main street that makes the best American dunkel weisse I've ever had. It's also driving distance to two MLS franchises, which should be an important factor in anyone's decision about where to move.
I've been to Bozeman and I didn't like it, but I didn't do much exploring either. It was a road trip stop. On that same stop we also stayed at Couer d'Alene, Idaho and that was nice. Duluth, MN is an interesting place to visit too.
I loved Bozeman until I looked at what real estate goes for there. Apparently it's been overrun by Californians. Butte is, oddly enough, my favorite town in Montana, but that's probably because it was snowing and all Christmasy charming and stuff.
It's an old logging town and still has that rough feel to it. As nancy said, it has a truck stop feel to it, especially if you wander through that main thoroughfare - gas stations and fast food places galore. A couple of streets, they have a little downtown that has a quaint charm. Obviously, the outdoors and the lifestyle it offers is the great draw of the place.
My boss just got back from a vacation in Vermont (he and his wife and two other couples stayed a week in Rudyard Kipling's old house) and they spent some time in Brattleboro. From the pictures and his description it seemed like a very, very attractive little town.
I spent some time in Northampton, MA and that may be what you are looking for. Beautiful old houses, good arts community and an hour N of Hartford, two west of Boston.
Portland, Maine I'd recommend something smaller like Camden Maine, or Bar Harbor, or a number of great towns in Maine, but they'd fall below your population minimum.