This is a great use of the iPad! Document cameras are excellent: especially in elementary classrooms. Suzy Brooks, a teacher in Falmouth, MA, has excellent examples of this on her blog: 3rd Graders Dreaming Big (http://blogs.falmouth.k12.ma.us/simplysuzy/)
Free video in video option for an iPad. Video can then be exported to camera roll and imported into iMovie for a profession video in video effect. The free version keeps a water mark on the video.
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.
Create a story with text, images, and video from your camera roll, Dropbox, and the cloud. Scroll through to read online and share. Interesting free option.
Though intended for the iPhone, this app could work on an iPad. It allows you to quickly and easily create a story by taking pictures. If you have a 3G enabled device, it also will geotag the camera roll. Could be great for field trips.