These days, I always have one of these on me. They are cheap, $15, but hold up just as well or better than my old Streamlight Scorpions, and are three to four times plus brighter. For what they cost, I have a bunch, and besides my pocket, I keep them around the house, in the car, anywhere I might need a spare too.
I thought it was well known now for years that these type lights were a weapon in their own right. Even the old, first to show up zenon type were pretty good, and years ahead of the old angle head or Maglight type lights they replaced, although they dont replace the Maglight for a good club. The new LED's are truly amazing. That little light above will shine a beam over a 100 yards and allow you to identify what it is youre shining it on at that distance and beyond.
Personally, I prefer the "one switch" (momentary, on/off) type that dont have all the fancy options. The "kiss" principle works best here for me, and I always know what the light will do when I hit the switch. The others Ive tried always seemed to have a mind of their own when turned on, and you never knew what was going to come up next, and were just to fiddly for a "weapon".