I finally bought and mounted a Planet Bike Superflash tail light after seeing so many recommendations here. Wow, it's bright. Tonight's ride home from work was the first time I used it. As I was riding up a hill, a car came up beside me and the lady driving yelled out "I like your light!"
I've had people comment on my headlights before but this was a first regarding tail lights. I was thinking of getting a Dinotte tail light but now I'll just stick with the Superflash.