I think the Arc AAA is my favorite and most versatile light I own. It is tiny (not much bigger than a AAA cell) rugged (accidentally ran through the laundry without harm) takes a single, ubiquitous AAA (obviously), and by adding a handy clip for a AAA Maglight will clip right to the visor of a hat brim. So it's a combo clip and handheld light. It has some sort of electronic circuit that boosts the voltage so it's a really bright light on a single cell.

David