pippin & merry
You can't really be sure about this one. In the movies they're not really together that much, because they get seperated in the middle of FOTR ( Fellowship of the Ring ). Though, from what I understand they are good friends, but not together as much like Frodo and Sam. Because they made sure they came along as the Fellowship, to help Frodo, knowing they were thought of as weak kinda, they didn't care. But it ends up throughout the stories, they aren't weak. And throughout the story, they're character builds up more and more. You never really know much about they're relationship, they aren't even together at all throughout the whole trilogy. They're only together at the beginning and the end.