If you're looking for a "be seen" light for city riding, I highly recommend reelights (www.reelight.com). They are mounted on the quick release and powered from

If you're looking for a "be seen" light for city riding, I highly recommend reelights (www.reelight.com). They are mounted on the quick release and powered from magnets on the spokes, so no batteries to worry about and a little more trouble to steal (the light can be removed by unscrewing the QR but the light has no power without the magnets)