I recently purchased an Amazon Kindle and was delighted to find many resources (Google Books, Amazon Popular Classics, Project Gutenburg, Archive.org) containing a trove of out-of-copyright books related to the Documentary Hypothesis and Source Criticism. Most are from the turn of the (last) century but still remain valuable resources.
The Documents of the Hexateuch
W. E. Addis, 1893
The entire JE text of the Torah + the Book of Joshua, with a lengthy introduction and copious footnotes. Helpfully notes contemporary scholarly consensus, or lack thereof.
Informative book-by-book overview of the OT, with a strong focus on the sources.
Who Wrote the Bible?
Richard Friedman, 1989
Seminal modern popular work on the Documentary Hypothesis. The arguments he makes are surprisingly in line with the 19th century scholars.
(Much more to come!)