I carry a Jetbeam PA20 in an old leather Buck knife case, that I modified by cutting the folding flap off. Fits in there very well and is always at the ready on my side. The PA20 takes 2xAA batteries wich are conviently available..
Same here two stinger led models with the piggyback battery charger
And a streamline knuckle head with the piggy back battery charger. I have them hooked up in my truck and they are always charging.
The best light hands down is the knucklehead it has an awesome magnet, it's like a five pounder and a swivel hook I love that light.. Worth every penny.
Flash lights! Now that is a tool just about worth it's weight in gold.
I have several flashlights which I use. I have an old school 2 AA maglite LED, a couple SureFires (don't use much because batteries cost to much) and my favorite is an Energizer 6 LED + Infrared head lamp. I get a lot of strange looks and even jokes from coworkers about exploring caves but 2 hands free + light where you want it can't be beat.
Dewalt 12 volt max LED. Clips to my Veto, has a magnet and the light head swivels in all directions. I often stick it on the side of the unit I am working on, or something metallic nearby with the light shining right on what I am doing. Battery life is awesome, and of course shares with my 12 volt max drill and impact (which is always in the Veto) so I always have 2 batteries wherever I am with my tools. Very bright white light.