I have one iPad in my classroom and I found one of the greatest app so far.
This app allows me to be around the room while writing on the projector. I can record my lesson and every stroke made on the iPad, that I then can download for students to lesson to again for reinforcement. These videos then can be downloaded to my website.
Here is a poster we made a few weeks ago in writing and below is poster that was made for math. Students were asked to write a story problem for the equation and I took pictures of examples to put on the screen with the strategies.
The app is free for the first 30 days and then it cost $30 for the year. Money well spent!