Rosslyn (i.e., the Key Bridge area) is just a couple of Metro (Orange Line) stops away from the Clarendon area of Arlington which has a fair amount of neighborhood-type bars, especially along Wilson Boulevard. Nothing really divey anymore (rents these days are just too high) and probably a few too many hipster-wannabes, but there are a number of decent places for a drink or few. When I first graduated from college there were still some nudie bars and "massage" places just up the hill from Rosslyn, but those days are long gone.
Clarendon bars