This is my area.
'Tactical' lights are intended for combat use by police, military, or anyone defending themselves. They are very bright, cast a perfectly white beam without any dim spots, and usually have a momentary switch on the tailcap for intermittent activation to light up the enemy without giving away your position like a constant-on light would. Soem can be had with remote pressure pads, like the one Steve is using. Great idea.
They are expensive, but nothing beats them for their intended application. They are often powered by lithium batteries which are capable of very high current output (for the brightest light for the size) and have very long shelf lives. Many of these lights have extra electronics in them to help regulate things so that you get maximum light output even when your batteries are running low.
The ones designed to be permanently mounted on guns are also insulated from the shock of recoil which would shatter a normal incandescent lamp's filament in a few shots. Some are using led's for extra reliability and for colored light, but have somewhat lower light levels.
When comparing brands, look for the lumen output. 65 of themis enough to temporarily blind someone in the dark, and is available in 6 volt lights that you can hide in your hand. If you want to upgrade, get a higher intensity lamp assembly or get a longer 9volt one that puts outover 100lumens.
SUREFIRE is the best, and has been making them for the longest.
http://www.surefire.com
There are many copies out there, and many are cheaper, most of them for good reason.
I want to put this bad boy on my bow. 3,000 lumens, and it only weighs 10 pounds!

You can burn up the fish without actually shooting them.
http://www.surefire.com/maxexp/main/co_disp/displ/prrfnbr/24279/sesent/00