Apparently, though Serenity was a flop in theatres, DVD sales have been so high that Universal may be considering another movie...
http://www.cinemablend.com/new/Serenity-2-May-Happen-6547.html
Banshee
http://www.cinemablend.com/new/Serenity-2-May-Happen-6547.html
Banshee