I currently use a Fenix L2D-Q5, but they don't make that exact model anymore. They *do* make the LD20, tho...
http://www.4sevens.com/index.php?cPath=22&osCsid=a03892cb23707cc76f59a7f539e2cc6b
That, along with a Two Fish Lockblock...
http://www.4sevens.com/index.php?cPath=92 .... will be PLENTY of light.
Most flashlights are NOT regulated, but these Fenix lights are. That means CONSTANT output. So if you keep it on 180 lumens, it will STAY at 180 lumens until the battery is drained in 2.25 hours.
You can also use the coupon code "CPF8" at the 4sevens store.
If 2 hours isn't enough time for you, then consider the Coast P7 flashlight...
http://www.amazon.com/Coast-Lenser-HP8407-Focusing-Flashlight/dp/B001AT1F6S More lumens and longer runtime, but it gets that longer runtime from NOT BEING REGULATED FOR CONSTANT OUTPUT.
I actually used that as my headlight until I was so drunk I couldn't ride my bike home one night, so my friends let some OTHER drunk guy ride my bike home that night. Long story short... he wrecked and the flashlight popped off. I do not remember any of this even tho I was supposedly awake. My friend put it in her purse and brought it to her house, where her roommate ended up taking it because she had a flashlight fetish.
SOOO.... I've never been able to compare the two lights side-by-side. But I remember that even after draining the battery overnight, the Coast P7 should still be bright enough for nighttime riding.