Anna and the King, the original work of Anna Leowens, the late 19th century governess for the children of King Rama IV, Thailand's most progressive leader who, with the help of Anna's feisty insight, brought the kingdom into this century. Don't miss the film of the same name starring Jodie Foster (though due to gross historical inaccuracies the film was banned from public release in Thailand).
The Beach, by Alex Garland, and the popular film featuring Leonardo DeCaprio, tells the story of young backpackers in search of the perfect hideaway. Following a map given them by a man on the edge, the searchers swim to a remote island (not far from Samui) and join a community of dropouts living in bliss on a beautiful, secluded beach, the sea providing the food and nearby fields full of all the ganja they can smoke. The story has become a popular model for the modern Utopia, and travelers in Thailand seem to enjoy the idea of a heaven on earth in the Thai south (and most find that today's overdeveloped beachfronts come up short). I like the way Khao San Road, the neon-lit backpacker ghetto of Bangkok, is depicted as mysterious and exotic -- quite the contrary. For another Utopia, check-out Emily Barr's Backpacker, another model for idealistic travel and soul-searching in Thailand.
I really like Tiziano Terzai's book, A Fortune-Teller Told Me. Though not about Thailand exclusively, Terzai offers a well-crafted portrait of the interlocking cultures of Asia, telling of how China's diaspora affects the region and painstakingly relating the interesting minutia of Southeast Asian culture in an autobiography of his search for personal destiny.
For help in understanding what the heck is going on around you in Thailand, pick up a copy of Culture Shock! Thailand by Robert and Nanthapa Cooper. Most bookstores in the West and in Thailand sell a host of useful phrase-books and Thai/English dictionaries. For more comprehensive study of the basics of Thai writing and speaking, pickup a copy of Thailand for Beginners by Benjawan Becker.
Asia Books, a Thai bookseller with outlets throughout the country, is also a small press publisher and offers some interesting and informative writing about Thailand and Asia in general. Stop by any of their stores in Bangkok or the larger tourist centers, and look for their titles in small kiosks at beachside convenience stores in resort towns. Carol Hollinger's Mai Pen Rai Means Nevermind is a personal history of time spent in the kingdom some thirty years ago, but the cultural insights are quite current. Patpong Sisters by Cleo Odzer and Sex Slaves by Louise Brown are both interesting exposés of the Thai sex industry. These are but a few of the many published by Asia Books.
The full list would be long, but below are just a few of the many books about Buddhism and the Thai Theravadan traditions: For the word straight from the horses mouth, try any of the writing by Ajahn Buddhadassa, a widely published Thai monk and founder of Wat Suan Mohk, an international meditation center in the south of Thailand. Buddhadasa's Handbook for Mankind and The ABCs of Buddhism are good introductions to meditation practice. Also look for writing by Jack Kornfield, an American who writes about meditation practices in works like A Path With Heart. Phra Peter Parrapadipo's Phra Farang, literally "the foreign monk," tells the story of an Englishman turned Thai Buddhist monk. A unique read.