If you're just diving recreationally in open water, then cheap Chinese torches ftw.
Here's what I use:
XTAR D06 CREE XM L T6 LED 800LM Diving Flashlight Torch Diving 100M Flashlight | eBay
It's $76 shipped with case, charger, and battery. 800 lumens, and under 6" long. That's small. I haven't seen another light that has the same brightness with such a small size. Aluminum body takes hits well and it uses a magnetic switch so the chances of the housing flooding are low. If you just want the light on its own you can pay as little as $65.
I know of an LDS that sells this exact same light "rebranded" (aka someone changed the label on the box and literally just stuck a sticker over the Xtar logo on the light itself) and they charge $180 for it.