Disclosed are various embodiments for identifying complementary items to items available for sale, lease, download, rent, etc. by different merchants in an electronic commerce system and presenting the complementary items alongside requested items in a user interface to improve a user experience when interacting with the electronic commerce system. The user interface includes a first user interface object that includes the requested items and a second user interface object that includes the complementary items to the requested items. The complementary items are displayed in the second user interface object in vertical alignment with a position of the corresponding requested item in the first user interface object.