The Surefire 6PX Tactical light came out a few years ago and I snatched one up after reading the specs and handling one in person. For those of you familiar with the classic aluminum body 6P, this is an updated version with a brighter, whiter light that will perform well when used as a weapon light or general purpose/duty light.
-Momentary on tail cap switch with only one brightness setting (200 lumens originally, 320 on the current version)
-Standard size body for use on most light mounts
-2 hour constant runtime (spec). My testing has shown it to go well beyond that time in normal weather conditions
-Has a bright focused beam while still producing plenty of ambient light for good situational awareness
-Weather resistant O ring to keep out moisture
-Cost. The 6PX Tactical may be among Surefire's budget line but it's not exactly cheap. They sell from between $80-120.
Here's a video with some shooting on the AR & AK platform, an illumination demonstration vs. a 104 lumen Maglite, and a discussion/demonstration of the light's pros and cons: