Tracker Item voted for.
One could use the Workshop module for this. I have my students grade one another using this module. It wouldn't be too hard to set up special roles for the grading process. Personally, I have a situation where I need for assignments to come in at various times and be graded at various times. For example, one could be submitting an assignment while another has already been graded by multiple markers. Workshop would not work in this scenario, since it has to move through separate phases which are triggered manually. Assignment with he capability to collect and display multiple grades and feedback for a submission asynchronously would be ideal.