I can tell you a few I know my teachers use:
I'm sure there are other apps they use but that's all I can think of at the moment.
If an entire campuses chooses to use a specific app then we will enable at the sub-account level for just that campus if it's only a few teachers then we guide them through integrating the app themselves. We have a handout with "tips" and this process is part of that.
Hope this helps a bit.
I would also add Quizlet! For the most part I tell teachers how to add the apps and then they add what makes sense for them. The exception would be something like Brain Pop where we have a district license. For these, I add the app at the admin level.