Knog Blinder V4 on the helmet, mounted sideways, very bright and noticeable.
However, there is a problem with this set-up. I wear a backpack, and when I'm in the drops or otherwise pretty low, I fear that the backpack may block drivers' view of the helmet taillight.
I have rationalized the situation by figuring that if I'm in the drops, I should be going fairly fast, but that sounds stupid even as I type it. Well, I have a blinky on the bike as back-up, and do monitor my helmet mirror constantly.
I'm struggling with the ideal setup too... I currently have a
Portland Design Works Danger Zone on
a-HA! Mode on the mount on the back of my pannier rack, and another one clipped onto my little Camelbak backpack. I'm also getting the
L&M Vis 360 for my helmet, and have the
L&M Urban 700 on my bars. The problem with my pannier rack-mounted tail light is that my Ortlieb bags probably obscure the light a bit from the sides (how important this is, I don't know). That said, the
Danger Zone is only $19.75 at MEC here, so I'm contemplating actually getting a third one to mount on one seat stay (with the included seat stay mounts), and then moving my rack-mounted one down to the other seat stay.
Overkill?