Since you did not specify exactly where in the Northeast, I really like the banana and all the other flavors at Hodgie's in Amesbury, MA.
It's made on the premisis, you can see them lifting the big paddles out of the chillers. Lines at each window have 12-14 people each. But it's oh, so worth it.
There's also a place in Ipswich down the road from the Clam Box in Ipswich, MA called White Farms. http://www.roadfood.com/Reviews/Overview.aspx?RefID=3798