Like said above the Cateye taillight is great, super bright.. I use a combination of lights, one to see and another to be seen.. The be seen light is Planet Bike beamer 3..
http://www.planetbike.com/frontlights.html#
The led flashes at a very quick rate, I would say about a 100 flashes per minute.. Cars will stop for a flashing light more so than a standard light..
Another way to go is mount a small flashing LED light on your helmet, that way you can direct the light at approaching cars.. I found this to work the best of all.. You can use a Princeton TEC aurora or the New EOS.. The EOS can also double as a decent light in a pinch, when used in standard mode.. I found these 2 lights to have the most adjustability when used on a helmet and the best thing is that they are very lightweight, right at 3 ounces w/ batteries installed.. You just need 12 to 18 inches of velcro with a loop, similar to a pump strap and your ready to go..
http://www.rei.com/online/store/Prod...cat=REI_SEARCH
http://www.rei.com/online/store/Prod...cat=REI_SEARCH
http://www.geocities.com/mar10stuff/...metwaurora.jpg