With help from the Birmingham City University we made an audio/video feedback plugin for the Moodle Assignment (2.3+) .
Using it you can record audio or video feedback for your students. If you like, you can even draw pictures or snap them from your webcam as feedback.
It is part of the PoodLL set of plugins, so requires the PoodLL filter to be installed. Until it goes live on moodle.org, it can be downloaded from the downloads page on http://www.poodll.com .