Here's my mapping from David Allen's GTD workflow to the parts in my system that implement each component. My main electronic tools are Things (http://culturedcode.com/things/ ), Journler (http://journler.com/ ), Mail.app and iCal. My main physical tools are my HPDA, my physical tickler file, my A-Z filing cabinets and my "inbox" and "pending" boxes.
(the workflow image is © David Allen & Co.)