Princeton Tec is starting to sell their new Swerve Rear Flasher. It is super bright and can be seen in the daytime pretty easily. They are using a 1/2 watt Luxeon LED with their proprietary collimator lens. The way it works is the bottom light is full force focused for distance. The top light on the other hand is reflected for more proximity light. The combination does not allow your eyes to rest and therefore seems much brighter than it is. I've gotten a couple of samples and have been very impressed on how bright they are. Check it out here.

Because of the battery drain on 1W and 3W (or for that matter the new Rebel and Cree LEDs), it just isn't pratical (according to Princeton Tec) battery-wise to use these LEDs running on 2 AAAs. They believe that the Swerve's combination, both LED and lens, gives this light the brightest output of any back flasher running on AAAs.

The other great thing about the Swerve is that it can be mounted in almost any configuration you can think of (bike rack, bike trailer, full suspension, large seat post, small diameter frame tubing, etc. etc.). This is one of the things PTEC focused on when creating the light. In fact it was the biggest complaint they received when investigating the lights currently available.