If you were to ask me my #1 iPad app, it would have to be Teacher's Assistant Pro. This app is by far the best organizational tool for classroom management. You can quickly and easily keep track of your students' behavior. I inputted my students, color-coded their actions based on my classroom rules, and added my own infractions. You can filter the results by the week, grading period, etc. Another cool feature is that you can email parents straight from the app. When you get that note wanting to know why Johnny's conduct grade is low, they are quickly notified. You can also export your data into a Google Doc as a backup.
At $7.99, this app is a little pricey, but I can guarantee that is is money well spent. Anything that will make your day just a little easier is worth a few extra dollars. The free version only allows for five students, so you may want to sample it. The pro version allows unlimited students that you can arrange by classes.
I have in no way been compensated for my review. When I find a great product, I want to share it.