I have last years model of the NiteRider MiNewt Mini-USB.
The battery is rechargeable by USB connector. The battery pack velcros to your bike, and the light itself is attached with a rubber band type thing. It is secure, but easy to swap between bikes, or mount on a helmet (if you buy the strap to do that). It is plenty bright enough for me and withstands heavy rain. You can check it out on Friday at FOC if you want.
It looks like the 2010 model is <$100.