Absolutely. You don't even need a crazy powered or expensive one.
My recommendation (which I think is pretty much unbeatable for price/performance) is to go with a LED flashlight:
Terralux 2 x AA ($28)
Romisen 2 x AA ($25-$30)
Fenix 2 x AA ($50)
Google them - they put out 200 lumens, which is bright enough to see with, even at 18mph, yet not bright enough to blind. I verified this again last night by shining the light on a pitch black road toward myself as I walked toward it - it definitely is not blinding unless you beam it directly into someone's eyes.
Mount it on your helmet with a rubber band (loop both ends through) or cut a length of inner tube and make holes on each end to slip the light through while looping the tube through the helmet vents. These methods are super-stable, and cost nothing.
After using the above, I have had no desire to upgrade whatsoever. I came across 3 riders using older-gen halogen fancy helmet-mounts that they said cost $300+ at the time, and my light was brighter and whiter than all 3 of theirs - and I have never had a problem with the mount stability despite its low-tech nature. Skip the bike-specific lights - they cost way too much (usually $80+ for 1/2-1/3rd the light output.)
This solution is AWESOME for street signs, or getting the attention of encroaching cars who you suspect don't see you and may pull into your path.
Nuff said.