Like you I have enjoyed the Batman trilogy that has rapped up recently with "The Dark Knight Rises" which was a good film. With the new Superman movie, "Man of Steel", coming out there is still talk of a Justice League film for the future. This in fact leaves several key characters without a updated and newer film to be released-Wonder Woman, Flash, Aquaman and Cyborg (if you want. Note-I have yet to mention the terrible Green Lantern film. There, I mentioned it.) With these characters in mind I feel that he next DC movie should be The Flash.
Now, why the Flash? Which Flash? Barry Allen I say. Its up for debate but that is later on. Why choose Barry Allen and the Flash to make as the next DC movie? Because of the Rogues and Barry is more relate-able and adaptable for the screen. With that said, what Rouges in specific? I propose Captain Cold, Mirror Master, Heat Wave, Trickster, Captain Boomerang and Pied Piper. With this group of Rogues you not only have great villains with great powers but you have compelling back stories.
The Flash movie should not be an origin story, it would take too much away from the film and you can explain it in a flashback. It should be where Barry has been the Flash for some time and has a foot hold on his powers and deals with the Rogues being a new thing in Central City.
Now how do you give credit where it should be do for the Rouges? More time and fluid story telling. If the Nolan Brothers can make a film that is over two and a half hours then why not do one for the Flash and use the time wisely?