I have to second the Light and Motion VIZ 360. I have a Vis 360+ in addition to a handlebar and tail light on my bike and I think it is great for visibility as

1) you get the amber lights for side visibility - many of the brightest tail lights and head lights are very narrow directional lights, offering poor side visibility. The L&M lights with these amber lights solve that and give people an idea of what direction the bike is facing based on different color lights.

2) THe light is higher up then on your bike, making it easier for large SUVs, etc to see you.

I strongly recommend one of these in addition to lights on your bike if you are willing to spend the money.

I have also seen a number of riders with the Light & Motion urban headlights and taillights on thier bike. these also have the amber lights and they seem very effective. I am planing to use these for my new bike.

I also saw a biker in day recently using the L&M VIS 180 tail light. It was day and as I pulled out to turn I immediately noticed him while looking as this tail light was very bright. Reminded me of the advantage of a good quality, bright tail light in the day.