A very cool tool! Voice thread allows you to annotate a slide show with audio files from multiple sources. A collaborative, multimedia, web 2.0, FREE web application.
This is a link to a nice little video/screencast made by students about
"How to Voicethread"
This is a pbwiki with lots of examples and information about Voicethread.
This is a one minute tutorial to get you started.
This is a Ning with some very good ideas for using Voicethread and links to examples in maths and science and english for various age groups.
Voicethreads could be a good way for a class to do a book review. I like this example, seems very achievable.