Learning in Hand features project ideas, classroom management strategies, and resources for teaching with mobile technology - including iPod touch, iPad, and iPod.
YouTube's response to Vine & Instagram, MixBit allows you to shoot, edit, and post video from your mobile device. Technically an iPhone/iPod app, it would work on iPad.
This product from the School Improvement Network facilitates administrative classroom walkthroughs in that it leverages the camera capabilities of the iPad/iPhone/iPod Touch and integrates it with assessment tools designed to give teachers constructive feedback.
Adobe Reader has some great features - such as inserting a signature or filling in forms. However, when sharing out completed forms or PDFs with annotations, the notes do not appear. It seems as though this is best used if annotating and then printing.