It is worth noting in any discussion about lights that batteries matter, a lot. I know somebody already mentioned that. I just wanted to emphasize the point and add the Sanyo Eneloops are the absolute best. I'm sure people will say they have had good experiences with other batteries (and I don't doubt them), but Eneloops are constantly raved about on photography and flashlight forums. Highly recommend them. They are just so consistent. On my two light setup, my lights usually die within 1 minute of each other. Predictable is comforting. All of the above only applies of course if you are using lights that take standard battery sizes. Some are proprietary. If it takes an 18650 lithium ion...buy Sanyo. (No I do not work for Sanyo, nor am I affiliated with them in any way).

Also...as a newbie to commuting in general but especially riding in the dark...I just want to say that NIGHT RIDING = THE BEST KIND OF RIDING.