Olight M20SX.
This thing is great. It is rated at 500 lumens using a Cree XM-L bulb, uses two CR123 lithium cells and have a nice aluminum body. I've had this mounted to my M4 for probably a year now and love it. One of the neat features it is comes with a glow in the dark on/off button on the...
back of the tube. The side button you see in the picture is the button that allow you to adjust the brightness when the light is on. If you press it with the light off, it offers a very fast and disorienting strobe.
Having used it for the last year, I would easily put this against ANY Surefire or Streamlight out there. Plus this was only $90. An equivalent Surefire would probably run closer to $300. Buy one, you won't be disappointed!