Running Form

I've been thinking recently of looking at a few aspects of training including ensuring my running form is good. (It'd also give me something to concentrate on during a race when things start to hurt).

Does anyone know of good sources of information? Books, videos, websites?

I'm thinking that stride rate and breathing are important, but what about body position etc? What exercises can be done to work on form? I've seen that a couple of books "Run Strong" and "Programmed to Run" might have something in them, has anyone any experience of these?

Any advice gratefully appreciated!