I follow quite a few blogs via Google Reader and one of them is KC Bike Commuting. When I was trolling a while back I saw a great hack and emailed Noah to give props and ask if I could post here. He kindly said yes. Enjoy and check out his blog for more good stuff. All text and pictures credited to Noah.
________________________________
Using a 5" long section of old inner tube, I lash my modified Mini Maglite to the handlebars of my road bike as a backup-backup headlight.
Take a 5-inch section of old inner tube (this one flatted years ago) and cut two holes through both layers using a pair of scissors. Make sure they're big enough for your flashlight to pass through. This is a 28mm inner tube. Much smaller than that, and this might not work too well.
Pass the body of the flashlight through one hole, then wrap the tube around your handlebar. Stretch the tube out and pass the tail of the flashlight through the other hole. Adjust angle accordingly.
More Flickr photos can be found here.

I'm wondering if the set up as is, is susceptible to being knocked off of pointing ahead where you want it?
Perhaps if you have your maglite resting on the hard surface of your bars, where it's not like to have much purchase, you could cut the length of tube longer in order to have it wrap around the bar once to give you a rubber surface on the top edge. Just thinking out loud. YMMV....
Posted by: Kymbo | 06/09/2010 at 06:33 AM
Just bookmarked this site-and this is a beautiful hack! Cheap and simple. I always have problems with the plastic handlebar slot thingies that come with bike lights-they break, they're easy to lose, so I wind up with a bike light that I usually just duct tape to my helmet. Not a good solution. I'm going to use this one!
Posted by: Brycemeister | 06/14/2010 at 02:59 PM
the symplicite iz magnificent
Posted by: jp | 08/29/2010 at 11:29 AM
That's a good idea! Thank you for sharing, i just want to find a convenient method to install flashlights on my bike.
Posted by: flashlights | 09/08/2010 at 09:13 PM
is it safey if you install?
Posted by: flashlight | 09/10/2010 at 10:45 PM