The PlanetBike SuperFlash is the gold standard of blinkie rear lights. I liked mine just fine, but I decided to try out the various super-bright bike lights for variety and because I've got a PlanetBike Rack Blinkie on my rack and don't like to have two lights of the same brand on the same side of the bike.
There are a few big huge plus points to be had here that the other lights in the product space don't have. First, it takes AA batteries instead of AAA batteries, which means a longer battery life for the same degree of power consumption and also simplifies your supply of spares if you've got a headlight that takes AA batteries. Second, it's got two half-watt LEDs, one of them focused in, the other one wide-angle. Wide-angle diffused LEDs are much more tolerant to being mis-aimed or viewed outside of their focused region... and I'd almost think that the non-wide-angle LED is somewhat useless. Third, the switch is much more convenient than any of the other lights I've seen. Instead of a little button, it's a switch along the face of the light that's easy to turn on by feel if you are riding around sunset.