Fusebox is the most used framework, used by 35% of ColdFusion developers according to the partial results of the State of the CF Union survey. The next most used are Model Glue, ColdBox and Mach-II each at about 15%. Note that the percentages don't add up to 100% because 1) people may use more than one framework 2) some people don't use any frameworks.
The survey is open for another few weeks, so if you haven't voted yet check it out. The survey also shows what versions of CF people use, databases used and common programming challenges.