The ReStore is on Raleigh Blvd. There's a map and directions on the website at http://www.habitatwake.org/restore/ I addition to doors, this place almost always has a load of structural lumber (2 X stuff), moldings, cabinets, and ... I could go on for a while. It's certainly worth a look. There's a partial merchandise list on the website in case it's to far to just drive.
Be forewarned that the free doors are thin skin hollow core interior doors. I have one to lay across saw horses for a light duty table for painting or what not. Used horizontally, they are easy to punch a hole in. Don't get me wrong - they are useful - but I would advice against getting one for anything other than really light duty use.