I was very unimpressed by Spice Market (though the visit was many years ago) and Salathip (the restaurant at the ShangriLa). I have heard nothing but mediocrity about Sala Rim Naam at the Oriental. For upmarket Thai dining, my BKK resident friends say Blue Elephant is the best bet -- not as tired as some of the other choices mentioned. I hear pretty good things about Celadon a lot too -- not great, but nice.