Simple publication workflow that enables the definition of the publication workflow for a given container or content type. The workflow itself defines what roles can create, edit & publish, and also how many validations are necessary at each validation step.
I second GadgetGeek's idea : custumized user notifications throughout the validation process would be very useful...
Also being able to send automatic customisable user notifications during the workflow process
Raymond de Jong commented
I think this is an essential part. Not as exciting as widgets or menus, but important to content management. For example, an editor should be the only person able to publish an article written by an author. What I imagine is an author logging on to the admin panel, and only seeing the menu items related to his permitted workflow tasks. This would make a good quality assurance and safety mechanism for the "documents" stored in the CMS backend when we're talking real businesses that in the real world need documents approved by legal departments or qualified persons.
Could this be done in conjunction with the Forms stuff?