Hi Scott,

I would have suggested something like the S81250 or
LP2950CZ5.0, as here

(16F88-based, a very high power bike lamp indeed)

http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif

from

http://www.siliconchip.com.au/cms/A_106372/article.html

s/w is downloadable from elsewhere on the site

Because of the generous overhead betwen battery voltage and 10F,
the parameter you'd be looking at would be quiescent current, rather
than LDO

I've used white LEDs for a bike lamp

http://home.clear.net.nz/pages/joecolquitt/bikelamp.html

and prefer them flashing. You do stand out more. Red rear lamp
is particularly more noticeable when flashed, compared to other
vehicles' non-flashing. For mine I used a basic bistable

http://www.play-hookey.com/digital/experiments/rtl_bistable.html

Companies like Maxim and Philips have a range of white LED
drivers too. These include DC-DC converters so that you can
run them off of just one or two cells

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