When most people begin looking for a luxury apartment rental in Manhattan, several districts tend to come to mind immediately. There's the sought-after high-gloss, high-culture vibe that comes with SoHo apartment listings, the famed luxury of Upper East Side rental listings, and the perpetually trendy East Village and its apartments for rent. But there's one New York City area of rapid growth and expansion that twenty years ago wouldn't have been on anyone's apartment-hunting list: Roosevelt Island. Once saddled with the less-than-flattering nickname "Welfare Island," this former backwater in the middle of the East River is an afterthought no longer, as a boom of new construction condos and luxury rentals on Roosevelt Island suggests. But here's the biggest sign of Roosevelt Island's rising prosperity: People are actually moving there. Quickly and in serious numbers. Seriously.