Most holes I deburr with a larger drill bit spun with my fingers. We're only taking off the burrs and being careful not to countersink the metal. Cautious is the name of the game.
Some blind holes will require fancy tools like this one mentioned earlier:
Originally Posted by SantosDumont
Edges, I have a scotchbrite wheel in my bench grinder and smaller ones on my pneumatic die grinder. The little ones are great for small areas, lightning holes or large skins that can't be brought to the bench grinder/scotchbrite wheel.