I'm a huge fan of the flashlights from Surefire. These guys take their flashlights very seriously. They are mostly aimed at military and law enforcement applications, so the stuff is very tough, insanely bright (they have a light that can blind you through your eyelids), and super functionally designed.
The 6P is the granddaddy of their lights and a personal favorite. It's a good size, bright (see above), and happens to be a good fighting light if you find yourself in a shootout in lowlight. (Doesn't everyone?)
They have very slick LED and weapons-mounted lights too. Their website and catalog are glorious and really show off their passion for excellence.
I love companies who really care about what they build, are honest about what they can and can't build (e.g. they don't claim their LED flashlight is visible at 20 miles and can last a lifetime on a single battery), and build great products.
Great, great stuff.