http://www.ikelite.com/lighting/flashlights/

They have a whole range of underwater lights... and they are darn sturdy.

I still have and use a Mini C halogen... that I probably bought some 20 years ago.

LEDs are much much brighter... so perhaps time for me to upgrade.

Along the lines of "go to" lights... I have a single AAA cell LED Maglight that I carry while racing... the amazing thing is that it is brighter than my old 4 D cell Maglight.
http://maglite.com/shop/flashlights/compact-flashlights/maglite-solitaire-1-cell-aaa-flashlight.html#.VK6_mHuYfT8

I've tied it with a loop to my multitool. I can remove it easily... but otherwise, it is always there. I coated the threads with vaseline in hopes of keeping the light working.