Though this is not necessarily a post specific to the iPad, many of the suggested resources either have apps or can be used on the iPad via a web browser. There are some interesting concepts for ELL/ESL or even foreign language learning.
This is an interesting app that seems to be a cross between Fotobabble and Animoto. The idea is that you can record ambient sound while taking pictures in order to create a short video. Could be an interesting way to document field trips or create a digital story.