Dancing Shrimp by Kasma Loha-Unchit. The recipes are very well tested. They turn out better than any Thai restaurant I've been to here in the San Francisco Bay Area. Now I refuse to eat Thai here in the U.S. if it's not home cooked. The only experience that has measured up is actually eating in Thailand.
My favorite Thai cookbook is Thai Food, by David Thompson, an Australian chef. Some of the ingredients were initially challenging to find, only because of name differences. A few items aren't available in my area at all, most notably certain fish and seafood. But once I figured out that long leaf coriander for instance is sold as sawtooth or culantro here, I have been able to cook just about anything from the book. With some simple substutions at times.
It's a rather scholarly book, with a whole chapter devoted to the history and cultivation of rice in Thai culture. I find that stuff very interesting. The book is laid out interestingly, with a menus chapter that has several courses meant to be served togeher. The street food chapter is fabulous.
The best laab I've made comes from that book and every salad I've made is wonderful. Every soup as well. The book may not be for everyone, but I love cookbooks that are so readable.
For everyday, after work Thai food I really like Nancie McDermott's Quick and Easy Thai. All of the fish and seafood recipes are wonderful and are the vegetables and salads. Great book for after work or a busy day when complex flavors are desired.