Google Docs Comments

If you use Google Docs you are probably already aware of how powerful its collaboration features can be.  They recently introduced an improved comment feature that has great benefits for the classroom.

http://googledocs.blogspot.com/2010/05/tips-tricks-comments-in-google.html

If you have students submit documents for review you can then edit, annotate, and comment throughout the document.  This provides valuable feedback to the student without cluttering up the document or having to tote around a stack of papers.