I use a PrincetonTec Quad LED, and I just zip-tie it by the base (which typically has an elastic strap for hiking/camping. 3-AAA batteries, waterproof, bright as all get-out, and weighs less than my Contour camera.
I think it cost about $30 at REI.
I'm also a believer in the "double up" theory.
I have my helmet light set to flash, and I use a generator driven headlight to see by.
In back I have a PDW Danger-Zone flashing taillight on my seat stay, and a wired, non-flashing taillight on my fender.
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"I feel like my world was classier before I found cyclocross."
- Mandi M.