Hi, I developed a very simple block (one php page only in fact) that list the assignment to be graded, for the course you are viewing (for grading-enabled user). It uses time marks to check this, and list all assignments that have not been valuated (graded or simply commented) by teacher AFTER last modify by student (timemodified>timemarked).
I'm attaching the block. At this time the strings (ex. title) are fixed in Italian, if someone find this interesting I'll make translations and put in module library.
Thanks for your hard work