The Darwin Correspondence Project is now making Charles Darwin's correspondence with some 2000 people available online. From the site:

Darwin's correspondence provides us with an invaluable source of information, not only about his own intellectual development and social network, but about Victorian science and society in general. They provide a remarkably complete picture of the development of his thinking, throwing light on his early formative years and the years of the voyage of the Beagle, on the period which led up to the publication of The Origin of Species and the subsequent heated debates.

The first available section is entitled "Darwin and Religion," which includes "Design in Nature," "Belief," "Ethics and Society," and the "Boundaries of Science and Religion." The "Darwin and Science" section of this project is still is under preparation.

  Charles Darwin at 51