Create a drop down list box that allows multiple selection

we have need to present a user with a run control type page that will allow them to select multiple deptids as part of the report criteria. It would populate the drop drop from a view on the department table, allow the user to select(highlight) one to many deptids, then use those deptids to build a Where clause for the report. We do not want insert multiple rows in a run control table and we do not want to use a grid with checkboxes on the page. Just a simple drop down list box that allows multiple selection. Anyone have