Probably the best of the ones I own is Thailand: the Beautiful Cookbook. It's a bit vague on some specialty ingredients but usually answers the question somewhere in the book. Make your own notes and cross-references directly in the cookbook the first time you go through it so you can find the answers again later.
I also get a kick out of book that combines a Chinese and Thai Cookbook together. Seems it was a special edition of two separate cookbooks. The Thai part is available separately as Everything Thai Cookbook. It streamlines, substitues and simplifies from authentic recipes but is still pretty good and accessible. Not a bad place to start if strict authenticity isn't your goal.
Do your shopping at an Asian grocer. Much better pricing and selection of ingredients as well as actually having things like galangal, kaffir lime leaf and so on. Coconut milk is also cheaper and usually a better brand. Mae Ploy makes good curry pastes but the tubs might be larger than you want to commit too. Taste of Thai is also good and more widely available in mainstream grocers but more expensive for less quantity.
The Best of Vietnamese and Thai cooking by Mai Pham is good- she is renowned and a personal client of mine so I have eaten her food- her restaurant Lemon Grass is excellent and has been written up in Food Arts and Art Culinaire magazines.
Also The Best of Thai Cooking by Amatyakul is good also.
thanks, we actually do a lot of shopping at the Asian grocer as it is....we have one of the biggest and best in the state about 1.5 miles away!!
went to the bookstore today to steal recipes (what we usually do on a sunday afternoon) Jean-Georges taste of Asia book wasn't too bad and Amazon.com: Keo's Thai Cuisine: Keo Sananikone: Books didn't seem too bad either. I think rather than recipes, we/she are looking for something that concentrates more on techniques than ingredient lists...while she does read them, she hasn't taken advantage of these message boards....yet...
That's a good chunk of why I said I didn't know of one I really liked.
There's a good chunk of Chinese influence in the cooking of Thailand so I see the techniques as closely related. The flavor profiles depart substantially though.
One thing I've learned is to let the curry paste break down and sizzle in fat to bloom the flavors. Very different than not having done so. Not that every dish is made with curry paste but for those that are, let it sizzle well.