We have had pretty poor luck trying to find lights that work well on the police bikes. The Nightrider jobs are sort of standard, but expensive, slow to recharge, and they don't run very long.
Battery-powered LED lights last for a long time, but often fly apart when you hit bumps or do anything violent.
I have just bought two sets of the new Blackburn "flea" LED lights to try out. These are mini (like, really small) rechargable lights with a clever system that lets you charge them from any 1.5 volt battery.
Supposedly, a "D" cell will give you 20 charges or so.
At first blush, they appear very nice. I'll let you know as they guys wring 'em out.