find the Assignment module very useful but it is missing a significant pedadogical feature - the ability to allow students to self-evaluation and to allow peer evaluation. The workshop module has those features but it is very limited in the "type" of quizzes or assessments that can be done. It also does not allow for the ability to give a time limit on doing the work. I would suggest that rather than have self-evaluation/peer evaluation be a separate module that it be integrated throughout moodle. Any work done by a student, the teacher should have the option of activating peer and self assessment.
Online assignments in particular modules would be ideal for such a feature.