When looking through Duke Universities use of ipods in their classrooms, I found a music class that was using an ipod to test students when playing music. The instructor would pull up the sheet music on his computer and the student would then play the song on his/her ipod.
I found lesson plans using ipods on apple's website. Most of the lesson plans involve using an ipod as well as a voice recorder. There were lessons that could be used on field trips, drama class and many more. The link to the website is:http://www.apple.com/au/education/ipod/lessons/