Either Surefire 6P or Malkoff MD2 with a Malkoff M61.
Another vote for this option. They're super reliable lights with good output and a simple interface. Just what a weapon light calls for, IMHO.
A couple of thoughts: The MD2 is already bored for the 18650, has a foward clicky, and can be had with a hi-low output ring that allows for a two-level output with the twist of the head. It's an outstanding light, and ends up being one of the least expensive of the high-output options.
The 6P with M61 used to be a good idea, the G2 nitrolon was even better, IMO. However, you need to add the clicky switch to get constant on, and have to find an older LED version since the latest models don't allow drop-ins. However, some people are reporting good results with the new G2X model.
Finally, just be sure your mount is compatible with the light you choose. The nitrolon lights are slightly bigger in diameter than the 6P series (incl. the MD2, IIRC) and this can present a problem for some mounts.