Definitely get a good light. I have run a lot over different lights while riding (not necessarily commuting) and I finally found one that is just amazing. Lights and Motion has the ARC light that can go on your handle bars or on your head. It is only 13.5watts HID, but it is super bright and burn time is over 3 hours on mine. There is nothing better than riding down the rode and being able to see your own headlight when you are in traffic with the cars headlights (that is how bright it is). You also have to remeber to turn it away from other cyclists if you are riding on a trail. I first got the light and watch someone cover there eyes (they had no light) and go off the trail into a tree.

The price is not cheap, but you can save about 25% if you find one on ebay (new).

I love the light, best money I have spent for cycling.