Arguably the two most well-known and best guide books on Thailand are the Lonely Planet and Rough Guide series. I have a preference for the Rough Guide series, but you pays your money and takes your choice. There does seem to be some inverted snobbery from backpackers and travellers in Thailand. Some sneer at the idea of a guide book whilst others cling to them as the fountain of all knowledge. There is no doubt they can be useful and even as a sometime resident in the Kingdom, I always have a copy of a guide book. Inevitably, some of the information can be slightly biased towards the writers’ own tastes or preferences, but in the main they are a useful tool if used in conjunction with a bit of common sense.
A selection of Thailand guide books can be found here.