I listed teams we have a rivalry with to varying degrees. Montreal will be forever but until we meet up in the post-season again or something akin to Chara pushing MaxPac into the stanchion happens it'll remain pretty dormant. Hell, to most of their fan base (Or at least the sub-30 age group) we might as well be Arizona, and without a mutual hate I wouldn't consider it a real rivalry.
Our rivalry with Detroit is essentially over, and I don't believe we have one with Boston (To answer a posters question).
That leaves Ottawa and Buffalo. I voted Buffalo because ever single time our teams play there is shenanigans, the teams don't like each other, their fans don't like us (Especially since we invade there barn routinely) and it's always entertaining. And frankly, I hate them more then anyone else.
What's sad it a mod added an option for some reason and it's gained more votes then Buffalo, Detroit, and almost Ottawa.