When in the market for a rail mounted tac light this is the way to go.. - SureFire X300 Tactical Handgun / Long Gun LED Weaponlight w/ Universal Mount, 170 Lumens

If a light is what you're looking for, you can't go wrong with a Surefire. Being prior military therefore already familiar with the name, I knew the quality that Surefire incorporates into their products. The only drawback to this light is that it's quite a bit longer than it's competitors--meaning that it does extend considerably further beyond the barrel than, for example, the tlr-1. Given that I carry a full size frame Glock this isn't much of an issue.
Pros: Incredibly bright(don't let the small package fool you), sits parallel with the bottom of my Glock20's trigger guard, very compact, lightweight, shock resistant even when putting hot 10mm loads down range, turn-key install with the standard gen 3 Glock sight rail(it even comes with a sightrail to install if your particular piece doesn't have one), the on/off switch is set up so that it can't be accidently turned on while holstered or stored.
Cons: Even on my full-size Glock 20 the light extends a good half inch beyond the muzzle. Fortunately my safepacker holster had enough extra room to allow for this. The price is STEEP(but worth it in my opinion).

This review was written in the old system and had content requirements that are different than reviews written today.