There are a couple of other ways besides the two-fish blocks too.

The cheapest and easiest is just interlock two hose clamps...cheap and secure

Fenix, a company that makes good flashlights also makes a handlebar mount.

This web page has a few other ideas.... http://nordicgroup.us/s78/flashlights.html

On that link above, scroll to the bottom of the page. There are some instructions on how to make a mount using conduit clamps. I have made and used these and they work well.