Justin at
ebikes.ca has made nice LED lights for ebikes using LM5009
buck converter IC from National Semi: " It's only good for 150mA but
for running a bunch of LEDs that is plenty of power. They also have a
350mA version in the LM5008. The chip makes it quite easy to design
the converter around, but it comes in a pretty fine pitch SMT IC that
is a bit of a pain for prototyping."