I ride a bikeshare bike for my commute so rather than rely on the front and rear led's built into the bike frame I prefer to add lights to my helmet. This time of year I don't use them but once it's getting dark out during my commute I will use them. I think helmet lights make you much more visible to both cars and pedestrians. I find the planet bike spoks are sized just right - I took them with me when I bought my latest helmet to see which helmet had vents in the right place to facilitate mounting. In the end I found a Nishiki helmet that worked best.

Here's a link to the lights on amazon

Amazon.com: Planet Bike 3042-1 Spok LED Light Set with 1 LED Headlight and 1 LED Tail Light: Sports & Outdoors