We have developed an assignment module that we find very useful. Full details are at the TutorBoard project site (including impressive screenshots).
Briefly provides a number of features to improve feedback assignment. The most prominent is that you can scribble directly onto the assignment. The most useful is that a marker can store predefined comments and insert them, if appropriate, at the correct location in the student submission.
It is very configurable, comes with complete source and documentation and I would say more but I'm rushing for a train,