"Varieties of Taoism in Ancient China: A Preliminary Comparison of Themes in the Nei Yeh and Other Taoist Classics" by Russell Kirkland is available here in PDF form. This is an essay discussing the nature of early Taoism in Ancient China and compares and contrasts its basic ideas as found in its earliest texts, which form the foundation of later Taoism. Kirkland argues that the text known as Nei Yeh (also spelled Neiye) or "Inner Cultivation", which is older than Tao te Ching, provides hints as to original Taoism before even the teachings of Lao-tzu and Chuang-tzu.