Before you go this summer, do yourself a favor and get a guidebook. And peruse it before you go. They have lots of suggestions and recommendations, and if they are from a good guidebook, they are typically spot on. And the sections on culture, history, arts, etiquette, geography, weather, etc. are invaluable.
There are a ton of guidebooks, from a variety of publishers, including Fodors, Rough Guide, Moon, and a host of smaller publishers. I am partial to Lonely Planet. The audience that they write for seems to be spot on with the type of travel I enjoy (going on a budget, exploring on our own, independent of tourguides and tour companies, going to out-of-the-way places where typical tourists are scarce, using local transportation, etc). Fodors seems to be targeting a more upscale traveller, and Rough Guides seems to target the backpacker crowd. Lonely Planet seems to be in a nice medium. (By the way, these websites have a LOT of good information for travellers, so they are definitely worth perusing.)
I have used Lonely Planet guidebooks exclusively, and haven’t been disappointed at all. The first one that I suggest is the general Thailand guidebook (click on this to get the Amazon.com webpage). It’s expensive ($18) and kinda big, but is a good source of general information on the country as a whole. Plus, this is a revised version, published in 2009, so it will have more recent information. Definitely recommended.
The Thailand book is a nice general overview, but it doesn’t give you as much information as region-specific books. Plus, you want something a little smaller for your daypack as you travel around. And Lonely Planet does have several regional books on Thailand. The ones I used the most are the one for Chiang Mai & Northern Thailand, and the ones for Bangkok. The one for Chiang Mai & Northern Thailand was very useful, as it has more detailed information on the northern part of the country than the general Thailand guidebook. Since we spend some time up north, near Mae Sot, this book may be worth looking into. Unfortunately, it seems to be out of print, and the only used ones on Amazon seem to be very overpriced. I do have a copy of this one, so you may borrow it.
The other region that we will be spending some time in is, of course, Bangkok. Fortunately, there are a couple of guidebooks specifically on Bangkok. Actually, they are two versions of the same one. The larger, more complete version, the Bangkok City Guide, is very good, with lots of information not in the general guidebook. It is kinda big, so they also came out with the Lonely Planet Best of Bangkok guidebook, a condensed version of the city guide that is smaller and more backpack-friendly. My wife used this extensively on her explorations of Bangkok with my (then) 7 year old son and 4 year old daughter. She recommends it highly.
Beyond these guidebooks, I also found the Lonely Planet World Food Thailand very informative. It covers in detail the cuisine of Thailand, including regional differences. It also has lots of hints on markets, street food, etiquette, food history, spices, and so on. It’s really a nice guide for Thai cuisine.
I’ll cover phrasebooks at a later time.