They'll probably go for the Justice League Unlimited route: The Flash initially can only run at the speed of sound, vibrate his molecules to phase trough solid objects and create tornados by moving his hands in superspeed. Maybe charge objects with kinetic energy in order to make them explode. Then, when he goes against Zoom, who is much more powerful and with a much wider array of superspeed tricks than he, the finally manages to break the speed of light and access the Speed Force.
And, judging by Greg Berlanti's comment that this movie will he "Part Thriller", I'm guessing we'll see a CSI-esque investigation movie in which both the policeman and the criminal have superpowers. The most fitting villains for this kind of approach would be Captain Cold, Mirror Master, Weather Wizard, Heat Wave and/or Murmur.