As above, need to be able to remove it from bike pretty quick/easy.
Lezyne lights are fantastic quality, easily removeable and in tests often come up brighter than their quoted lumens.
http://www.wiggle.co.uk/lezyne-power-drive-xl-front-light-1/
A road light or an offroad light? Already got any? (reason I ask is that I'd probably rather get 2 cheaper offroad lights than one better one)
buy my glow worm x2 thats for sale in classifieds 😉
Front or back?
For seeing or being seen?
Try the KK-Lights on amazone. They're very cheap copies of lumicycle lights.
Front for seeing
SolarStorm U2 off EBay and a Smudge battery?
candbseen 1200 lumen jobbie with the uprgaded heavy duty battery.
More than enough light for anyone
I got a set of two cree led lights off ebay (about £20)for the commuter bike, swapped them onto the mountain bike as better than the Hope one I was using!
The batteries last longer and the brackets dont break every couple of weeks like the Hope ones where.