Of course, Taoist classics come first: Laozi (the true classic of morality), Zhuangzi (the true classic of southern China) and Liezi (the true classic of Xu Chong). Then there are Wen Zi, Guan Yinzi, Huangdi Neijing, Guan Zi and Bao Puzi. Sometimes Huainanzi is also included in Taoism, although it originally belonged to a saint.

You talk a lot about classics, but you ask Taoism, so the books above are more important.