Someone has posted this lovely documentary about Henri Cartier Bresson. Bresson is undoubtedly one of the masters of photography and this revealing documentary is absolutely fascinating. He was a master of the decisive moment.
Also speaking of the decisive moment, this actually might just be an artifact of the past. Consider the notion that in the future your video camera will shoot such high resolution imagery that you could just record a long scene and then scroll back frame by frame to pick out the decisive moment! Kevin Kelly posted about this idea recently. He calls it the decisive hour. The main idea is that the distinction between cinema and stills is already gone.