I have one of these mounted vertically behind my seat bolt-- bright and lots of settings--I like the Night Rider one:


I also run a white Knog on my right fork blade. They are really bright and the batteries have lasted thus far for 4 months w/o substantial dimming. I'll probably change it out soon.

I have never really had a problem seeing at night in Tokyo (but hey, it's Tokyo). And there are no potholes or broken glass to speak of, so I'm not too worried there either.