I use the LD-600 modified to bolt to the top of my 'Topeak' seat bag and it seems plenty bright to me. I also use a small 3-LED "blinkie" light clipped to my Timbuk2 daypack and the combination of the two lets me be seen very well at night.

But I want more, and so I'm considering the "Superflash" to add to the mix, based on the positive reviews I get from the forums.