If you want bright you should check out/revisit these threads:
http://www.bikeforums.net/showthread.php?t=50863
http://www.bikeforums.net/showthread.php?t=42629
my light:
I'm running a 12V 4.0ah lead-acid, and a 20 watt philips spot MR16 bulb, gets the job done well. I have rode for about 2 hours max so far, the battery was still going full strength. Though this is a bulky setup and all the gear weighs about 5 lbs.