The new Princeton Tec Swerve is my new favorite bicycle tail light. It features 2 half watt super bright LEDs, a multitude of mounting options, and a great big toggle switch for easy on/off operation.
Princeton Tec introduced the Swerve light at the Sea Otter Classic last weekend. My biggest grip about most bike lights is lack of flexibility in mounting them. Princeton Tec has solved that problem with the Swerve, which has the best mountain system of any light I've seen, with a clip, brackets and multiple bands allowing you to mount the Swerve to just about any surface on your bike, your bag or your helmet. Princeton Tec even wants your photos of your unique mounting technique at the Swerve Your Bike website.
With a pair of half watt LEDs (either flashing or persistent), the Swerve is brighter than the Planet Bike Superflash, which has a single half watt LED along with smaller flashing LEDs. According to Princeton Tec, one of the keys to the Swerve's effectiveness and visibility is that the LED's have different collimators (lens) - one is diffused, while the other is focused. This creates two different beams patterns that the viewing eye has to juggle. Enough light diffuses through the transparent red case to provide effective side lighting, also. The LEDs are bright enough to catch the eye even in daylight and through fog.
A nice usability feature is the large toggle switch, which is very easily accessible and easy to operate while on the go. You can even flip the lens around to move the toggle from left to right if you want. I started my ride home from Monterey last Friday evening in daylight, but as dusk approached I reached around my seatpost and my fingers quickly found the toggle switch.
My only gripe -- and it's fairly minor -- is the relatively slow flash rate compared to most modern LED tail lights. I really like the super fast flash on the Planet Bike Superflash, for example.