I use one of these in addition to a reflective vest:
http://www.northerntool.com/webapp/w...9974_200199974
It uses lotsa juice, requires a sturdy mount, but gets the job done. The brightest SAE category. Several positive comments from motorists. With an amber light there is less concern about getting hassled by the police. Red flashing lights are permitted only for fire and police vehicles around here, but amber is basically unregulated.