by the by... did you get your screen name from the Gorillas of the same name?
there are several main branches of Taoist thought which are currently extant. typically speaking, these are divided into the religious forms of Taoist praxis, which are still mostly found in China and the surrounding area, the Philosophical Taoism, which is often what we find in the non-Asian countries and, the Spiritual Alchemy schools, which can be found throught the Taoist practicing world.
given this, there are several texts which are considered primary material, depending on which particular school that one may actually practice.
The earliest known Taoist text seems to be the I ching, well known as one of the fundamental classics of Chinese thought. This text was well regarded by both Taoists and Confucians. The I ching was written during a time when divination was prominent.
The Tao Te Ching is, without doubt, the most well known after the I ching. The Tao Te Ching is credited to Lao-tzu (Old Master) in roughly 600 B.C.E.
Other texts include Yin Convergence Classic, which is credited to the Yellow Emperor, an historical-mythological figure of ancient China, in roughly 2,500 B.C.E. Other texts include,Chuang-tzu, which is widely held to be one of the best literary works in history, Sun-Tzu a military strategy text, and Huai-nan-tzu.
The teaching of the Tao are easy to see, the words are supposedly easy to understand, but to actually "see" the Tao is an other subject entirely. This is "explained" in the first chapter of the Tao Teh Ching.
The Tao Teh Ching is not a Holy Book, it is but paper that can be thrown away, something to be used as kindling for a starting a larger fire and in a pinch can be use to wi.... well we must not use that type of language in good company.