How to create a drop-down list and be able to select more than one entry.

I would like to do this, too. How can it be done? Data integrity is not an issue down the line as long as data is there in the one cell. Just need a checklist where end user could pick multiple entries out of a picklist 6 deep. I except each entry would go on it's own line within the cell. Seems more efficient to allow this rather than any of the work-arounds suggested.