There are lots of "member of animal species X befriends member of species Y" but this story of Suriya (orangutan) and Rosco (dog) is possibly the best yet:
http://pbh3.tumblr.com/post/269075871/orangutan-and-dog-become-best-friends Watch the orangutan's behavior when he's not directly interacting with Rosco, too. He reminds me of an antsy hyperactive kid.
(thanks
dentage!)