The White Sound Defense FOSSA-556 is one of the most effective flash suppressors that I have used. On a 16″ barrel, it generally produces zero visible flash and it has the additional benefit of providing some muzzle climb mitigation. It is a very cool muzzle device that I like to talk about whenever possible.
White Sound Defense is giving one away and entering is easy. Just head over to the contest page and complete the two steps required to enter.