1st, I'm a flashlight freak, I own damn near all them, I could go for a week with all the lights that I have without recharging.
1st question, rechargeable or lithium Ion. Rechargeable is cool.
2nd, how big, since you want to operate it with one hand, small.
3rd, LED or Xenon, nowadays, LED have come so far, it is the way to fly..
4th, going back to the 3rd question, how bright, does it matter if you have dim down capability? Or strobe??
Best new lights on the market, in a small bright package, Streamlight scorpion, in LED, but it takes cr123 batteries, 4 bucks at walmart and it takes 2, good for an hour and a half, but good for 10 years left on a shelf. 40 bucks.
Streamlight Strion, rechargeable,, LED, compact and good for and hour and a half, more expensive though, internet, 90 - 100 bucks.
Insight technologies typhoon 1 & 2, 135 - 250 bucks with the dim down feature and strobe + up to 150 lumens., ultra bright, uses cr123 batteries. Has a built in finger rest for pistol shooting, holding the light in the weak hand.
Surefire, lumimax L1, 10 to 65 lumens and very efficient, very small and well built, 135 bucks, takes the cr123 battery, I carry one every day.
Surefire g2 Led, 65 lumens of white light, takes cr123 batteries, and is a great light for about 65 bucks.
Surefire, aluminum combat light, with lanyard and finger control for weakhand hold, 135 bucks and takes cr123 batteries.
I'm sticking to your criteria for offhand manipulation.
Best bang for the buck are the 1st 2 streamlights and the surefire g2 Leds.
My main carry light is a Streamlight stinger XT rechargeable, but it is a larger light, not too big, but too big to carry in most pockets. Since I use it everyday, the rechargeable makes sense for me.
Many, many choices my man, I own all of the above and they work for me.
Very glad you did not ask about weapon lighting systems.
By the way, if you have a mini mag light, the conversion is worth the cost, it elevates this little light, and is quite useful.