1. A method, comprising: receiving a first content set from a first content provider, wherein the first content set comprises at least one or more content objects having content-identifying information; receiving a second content set from a second content provider, wherein the second content set comprises at least one or more content objects having content-identifying information; receiving first social graph information from a first service provider, wherein the first social graph information identifies one or more users associated with a first user via the first service provider and the first social graph information includes one or more of: a separation metric that indicates that a second user is two or more degrees-of-separation away from the first user; and a group identifier that indicates that the second user is a member of a particular group associated with the first service provider; determining that the second user identified in the first social graph information has performed a first action associated with a first content object in the first content set; selecting, for inclusion in a third content set for the first user, at least a portion of the first content set and at least a portion of the second content set, wherein the selection is performed based at least in part on an identity of the first user and the first social graph information received from the first service provider; wherein said selecting includes selecting the first content item for inclusion in the third content set; based at least in part on the first action, determining a position in the third content set for the first content object; wherein the position is further determined based, at least in part, on the group identifier or the separation metric; and sending, to a client computing device that is associated with the first user, data that is based on the third content set; wherein the method is performed by one or more computing devices.