The Record of Tungshan, the founder of the Caodong (Soto) school of Zen; Cultivating the Empty Field: The Silent Illumination of Zen Master Hongzhi; The Recorded Sayings of Zen Master Joshu; and Master Yunmen. All are excellent, and with the exception of Hongzhi, are masters from the Tang dynasty, the "golden age" of Ch'an. Unfortunately, the first and last are out of print; I managed to find a copy of Yunmen on eBay, and a digital copy of Tungshan on Google books for a very reasonable price.
The ancient masters, I find, are more helpful than modern writers, many of whom, in my opinion, simply recycle the same message over and over again. The Zen market is saturated with dozens of books by modern authors, few of whom contribute anything new to the Zen canon. These Chinese ancestors, however--along with Linji, Huang Po, Baizhang, Mazu, Dahui, and Korean masters like Chinul--strike deep to the heart of the Dharma in a way few contemporaries can or do.
Read and savor these books; they are distillations of some of the greatest spiritual wisdom China has to offer. At first, their teachings may seem puzzling, paradoxical statements, but the more you read and digest them, the clearer their teachings become.
When reading these masters, we must remember that their teachings are upaya (skillful means) and thus are more pedagogical than philosophical. Our minds, sticky as they are and ever eager to grasp at something solid, inevitably try to turn the masters' statements into something concrete, some absolute statement. But that won't work because the masters are not making philosophical claims; they are trying to wake students up, because the Absolute transcends all words and philosophy. The teachings are fingers pointing at the moon, the great, perfect reality which is ever present. And as their teachings reveal, all we need to do is stop thinking and open our eyes.
For example: These four Zen masters, all pointing at the Great Moon of Reality, are they the same or different? Are there four fingers or one?
Have a great week.