Hi All,
There has been plenty of discussion about DealExtreme. Why not get their purpose-specific bike light? I have this and love it for any speed you want to go. There's a review in the MTB Forum as well: http://www.mtbr.com/cat/accessories/lights/magicshine/mj-808/PRD_448565_130crx.aspx
There's a video review somewhere in this site as well.
Deal exteme link (takes 2-3 weeks to arrive): http://www.dealextreme.com/details.dx/sku.25149
US local source (much quicker and not much more expensive): http://www.geomangear.com/index.php?main_page=product_info&cPath=4_41&products_id=138
I think there's another thread on lights somewhere in ES, but I couldn't quickly find it.
As someone who does a lot of night commuting, my advice:
1. Get a REALLY bright light for your handlebars. Cars will give you double the space they'll give you if you have a wimpy light.
2. Be nice if possible and keep the beam down if you are on bike trails with oncoming riders/walkers.
3. Unless you're mostly on straight roads/trails, get a helmet mounted light as well. My favorite is the small Exposure light, but it is really pricey. (>$200 USD)
If you are serious about bike lights, the MTBR forum has the most exhaustive list I've seen. Again, most of them are of the expensive variety