Three Animation Design Apps for iPad

Animation Creator HD (Full - $1.99 / Lite - Free)
I have been pretty impressed by this frame-by-frame animation design application.  The interface is very user-friendly, and with time and attention you can create some really elegant animations.  As you add a new frame, a 'ghost' of the previous frame is provided so you can manipulate the subsequent frame accordingly.

It is easy to import images and draw objects. Some downsides include a lack of an audio component and the fact that you can only export the video file to YouTube.

Animation Creator HD for iPad. Look closely to see the ghost of the previous frame.

Animation Studio ($1.99 - iPhone compatible)
The interface is a bit clunky. It took me a while to figure out how to add new frames and test out the movie, but I think if someone spends enough time understanding it there is potential to create some pretty snappy movies.  I especially like the ability to compose your own soundtrack using instruments and layers built into the program.

Animation Studio for iPad/iPhone. Compose music and record voice for the animation.

PhotoPuppet (Full - $3.99 / Lite - Free)
This is my third or fourth time mentioning this app since I started keeping track of my investigations on this website.  The simple fact that you can animate objects without needing to do frame-by-frame design is a huge benefit, especially when thinking about having kids design animations.

One feature that I have mentioned to the developer that would be great is the ability to import sound clips and songs.  You can record voice narration, but it would be a fantastic to be able to add sound effects and background music.

PhotoPuppet for iPad. Each object has an independent layer that can be manipulated.

Photos taken from the iTunes store website page for each app.