There are several sites that give recommended iPad apps to teachers. Here are a few:
But if you want to know what apps I have used today – on 9/14/2015, the apps are
Although there are 100,000’s of Apps, you will find that only about 5 to 10 are regularly used by you and your students. Ideally, you can treat Apps like books – and that is an educator should explore a new one (a new app) each month. It’s easy. Just go to the App store and then search on a topic like “teacher organization” or “student chat”.