I use to work for a noted flashlight company...
It is very important to understand the situations you will be working in to use a flashlight for photography. Are we talking about adding some highlights within the frame? Are we using it as a key-light to get focus, and switching it off for the actual shot? Are you just looking to bathe the scene in light?
Most of the work in field photography these days is in the off-camera flash department (check out David Hobby's Strobist for some excellent resources). Not so many people are using flashlights to light scenes, but with the power output on LEDs getting so good; I could see it becoming a more common occurrence. It's something I've looked into (casually) at Luma.
You'll need to think about a few things:
Power:
Measured in Lumens. Anything under about 100 is not going to be great for photography use. That's OK because getting 100 lumens out the front of a light these days is pretty trivial (just a few years ago, a 2 CR123 cell flashlight with 100 lumens was considered super bright; now keychain lights do that).
Beam Profile:
For photography, this is easily as important as the power output. At one end of the spectrum, we have "Thrower" lights, with focused beams designed to push light out in a very narrow cone and illuminate distant subjects. At the other end are "Mule" lights - literally just a bare LED at the end face of the light with absolutely no focusing. Most EDC/Tactical/Common flashlights are a bit of a hybrid, with reflectors engineered to produce both a narrow throwing beam (the "hot spot") as well as a wider area for illuminating around you ("spillover).
As I am sure you can imagine, the beam profile will have a profound effect on a light's utility for photography, especially on near subjects. You might want a narrow beam for the effect in a photograph, or you might want a mule light to add illumination scene wide. A narrow beam is easy; a mule light requires a LOT of power since it's energy is spread out in such a wide fashion.
Temperature and CRI:
With editing what it is now, I don't know that these are really critical factors unless you plan on some sort of zero editing (even the AP allows for color correction though). LED's all emit blue light (so very high in the temperature range) and the diodes are treated with a compound that filters that light to yellow. More of this filtering compound brings the color temperature down and color rendering index (CRI) up... but always at the expense of light output. If color temperature and CRI are important, you will be giving up power to get it. Having said that, color correction is easy with digital photography, so collecting the raw pixels may very well take priority and you can fix it in post.
Price wise, I would buy a few different low end lights to experiment and see what works for you. Fenix and 4Sevens are, I think, at the top of the quality pack when it comes to reasonably priced, high quality, well supported lights.
If you want to step up a bit in quality, SureFire, Elzetta and Malkoff Devices are making stuff that will blow the Chinese brands out of the water in reliability and quality, but also price. American flashlights are almost all focused on military/police use (since those are markets that spend money for quality); that means they will have high output with throw-focused beam profiles that have well engineered spillover. They are excellent, but it might not be the kind of light you want for photography.
At the very high end, custom makers can build you precisely what you want. Custom made throwers are easy to come by, custom made mules are also easy. If you want a hybrid beam deal though, the engineering to do proper reflectors is simply beyond the scope of most custom makers (there is a lot of simulation software involved, and very precise parabolic machining, finishing and often optics engineering involved). Having said that, I own one McGizmo Titanium Mule light with a daylight temp high CRI LED... and it's amazing.
