Well, lights seem to be a very personal thing but I'll share my most
recent setup with you anyway. I now use a Tiablo A8 Q5. You can read
a description at http://www.batteryjunction.com/specialeditiona8.html
It runs at 250+ lumens for a little over 2 hours on a 18650 lithium
ion 2600 mAh battery. The output is virtually flat at 250 lumens over
the entire 2 hours. I recently changed my commute route so that I now
ride along several unlit stretches of roadway where I can hit 35 mph
or so on the down hill stretches (if you are familiar with O'ahu, I
teach at the University of Hawaii at Manoa and live in Kailua near
Castle Hospital - a 22 mile ride along the coast past Haunama Bay and
Makapu'u) which is why I was looking for a brighter light. I had to
make a custom mount to fit it on my bike below the front rack but that
was not much trouble. I got it with the orange peel reflector, but
even so I didn't like the light distribution pattern so I cut a lens
off an old bicycle light and epoxied it onto the front of the light.
The resulting light pattern works quite well.
You can see a picture of the mounted light at
http://home.earthlink.net/~john.wendell/images/light.jpg I am quite
satisfied with the result. 250 lumens is so bright that I can see the
road surface very well and far enough ahead to have plenty of time to
react even at 35 mph. It is so bright that when cars approach me from
the rear I don't notice an appreciable improvement in what I can see
of the road surface due to the extra light from the cars. It also
gets oncoming cars to dim their bright lights, which is nice. I also
like that it is water-resistant and self contained (no external
battery packs and wires with connections to fail). The low setting of 100
lumens is more than enough enough to allow you to be seen in well lit
areas if you need to conserve power for the unlit stretches. It
weighs 150 grams and the battery weighs 45 grams. I didn't weigh my
custom mount but it is probably around 50 grams. I carry an extra
battery just in case but so far I haven't had to use it.

Aloha, - John