This is a pair of Tree Swallows - male on the left and female on the right.
Tree Swallows are not revered by many birders - especially those who have Eastern Bluebird boxes. True - they are little toughies and do try to displace bluebirds. But they are pretty aerodynamic to watch, and are downright pretty besides. At a recent banding we got a pair - here is a female in hand.