Shouldn't be too hard to find something, I've got got an easy recommendation and some outside the box. May depend on your setup, tank size, tank cover, etc. But here's some examples, prob more shoaling then schooling but certainly interacting with each other:
Anthias (My fav - Lyretail, 1 male, 4-6 females)
Group of Gudgeons (hang out at the top of the water column)
Cardinals
Even a big group of Skunk Clowns (Melevs reef has a group in his 400, they are always interacting with each other)
Reef Chromis (prob too mean though)
If I think of more I'll let you know.