Though not free ($1.99), this is almost like an entry level screencasting app where students draw and then tell the story about their drawing. Completed projects can be shared.
Animoby is a sort of screencasting tool, but not really. The idea is to instantly create and publish products that include voice, drawings, and images.
Create comic books and illustrations that include monsters and superheroes. The images and drawing tools can be used for a variety of literacy & numeracy activities as well as storytelling.
This free app lets you create notebooks that incorporate audio, drawings, type, and images.Its goal is to mimic a paper desk and become a notebook replacement.
This app, for $4.99, allows students to create their own animations. Though the app has an associated cost, the web version (http://doink.com) is free. Unfortunately, the web version won't run in Safari on the iPad. Cool regardless.