The best bookshops in Bangkok are Asia Books, on Sukhumvit Road near Soi 15, and DK Books on Surawongse Road near the infamous Patpong Road area. Asia and DK also have smaller branches in some of the larger tourist hotels in Bangkok and street branches in tourist towns like Chiang Mai and Phuket.
In Chiang Mai, Surawongse Book Centre on Si Donchai Road is also very good. All of these bookshops specialize in English-language publications and offer a wide variety of fiction and periodicals as well as books on Asia.
Two travel guides with some good stuff on history, culture, art, etc., are Nagel's Encyclopedia-Guide to Thailand, an expensive little book published in Switzerland and Guide to Thailand by Achille Clarac, edited and translated by Michael Smithies.
The Insight Guide to Thailand (Apa Productions, Singapore) is beautifully presented and well written although it's a little hefty to carry around as a travel guide - a worthy item for travel guide collectors at any rate.
If you can get hold of a copy of Hudson's Guide to Chiang Mai & the North you'll learn a lot about this area that is unknown to the average traveller. Much of the information is out of date (since the book is long out of print) but it makes interesting reading and has one of the best Thai phrase sections ever published - 218 phrases with tone marks. (Phrase sections without tone marks are next to worthless.) In 1987, Roy Hudson published the minuscule Hudson's Guide to Mae Hong Son that you may come across in the north.
Recently a number of locally produced Thai guidebooks have emerged. The Shell Guide to Thailand is basically a directory of hotels, restaurants and service stations but provides many useful addresses and phone numbers and has some good maps.
If this is your first trip to Asia, you might want to have a look at Before You Go to Asia by John McCarroll (Laurel Publications, San Francisco). This book weighs the pros and cons of going on your own versus going with a tour group (the author comes out strongly in favour of going on your own) and lists references for further information on Asian travel.
If you are interested in detailed info on hill tribes, get The Hill Tribes of Northern Thailand by Gordon Young (Monograph No 1, The Siam Society). Young was born of third-generation Christian missionaries among Lahu people, speaks several tribal dialects and is even an honorary Lahu chieftain with the highest Lahu title, the 'Supreme Hunter'. The monograph covers 16 tribes, including descriptions, photographs, tables and maps.
From the Hands of the Hills by Margaret Campbell also has lots of beautiful pictures.
The recently published Peoples of the Golden Triangle by Elaine and Paul Lewis is also very good, very photo-oriented and expensive.
Additional serious reading is: The Indianized States of South-East Asia by George Coedes - a classic work on South-East Asian history; The Thai Peoples by Erik Seidenfaden; Siam in Crisis by Sulak Sivaraksa, one of Thailand's leading intellectuals (available at DK Books in Bangkok) and Political Conflict in Thailand: Reform, Reaction, Revolution by David Morrell and Chai-anan Samudavanija, probably the single best book available on modern Thai politics.
Culture Shock! Thailand & How to Survive It by Robert and Nanthapa Cooper is an interesting outline on getting along with the Thai way of life. Letters from Thailand by Botan (translated by Susan Fulop) can also be recommended for its insights into traditional Thai culture. Cooking Thai Food in American Kitchens by Malulee Pinsuvana is 'great because it has pictures and diagrams so you can identify your meals'!
For insights into rural life in Thailand, the books of Pira Sudham are unparalleled. Sudham is a Thai author who was born to a poor family in northeast Thailand and has written Siamese Drama, Monsoon Country and People of Esarn (Isaan). These books are not translations - Sudham writes in English in order to reach a worldwide audience. These titles are fairly easy to find in Bangkok but can be difficult overseas - the publisher is Siam Media International, GPO Box 1534, Bangkok, 10501.
For books on Buddhism and Buddhism in Thailand, see our religion page.