Rummynose Tetra from what little I've seen school fairly close. Corys are always fun to watch. I love them to death as I have three different species and am most likely planning on getting a 4th as soon as I get another tank cycled and set up.
Loaches are known to interact with each other and other fish often. It is entertaining to watch them have little play fights over food, or clean the any food particles off the side of another fish. Sometimes, especially when kept with no other loaches, they will school with other fish species. For example, years ago I had a single clown loach who liked to school with a large group of tiger barbs. In some cases, loaches are so interactive that it becomes a problem, as slow and delicate fish become stressed and bothered by the loaches activities.