I have the PBSF (Planet Bike Superflash) with a rear rack mount. It is sold separately, but should be available at your LBS for $5 or from Amazon for $4.50 with super-saver shipping: http://www.amazon.com/Planet-Bike-Ta.../dp/B000IQEAK2.

I've never had problems with the light coming out of the rack or coming apart, but perhaps the road conditions here are not as bad.

However, the Radbot 1000 looks like a great light, and you should probably get that instead of the PBSF if you want to mount it to a rack and you need a super-bright flasher for daytime use.

The B&M 4D Toplight has a much large reflector (which is very important if you every forget to turn on your lights) and is available in a dynamo-powered version. I think these European style rack lights look much nicer than the tiny blinkers (which are designed around seatpost mounting), but I have no idea how bright it is. I have an older model Toplight on my Breezer, powered by the hub dynamo, and it's great to have a light with no need for batteries. The wiring for the rear light is not that bad, and may be worth it in the long run. And you can always have the PBSF or Radbot as a back-up or flasher, with the dynamo light on steady.