Daybreakers has an interesting take on the vampire genera, which in this case the world (or just the USA? hard to tell) is completely overrun and ruled by them, making the human race almost extinct, but the vampires still need their (our?) blood to survive and not mutate into a mindless giant bat. A good vampire Edward Dalton (played by Ethan Hawke) is desperately trying to synthesize a blood substitute so they can stop depending on human blood.