In my LA Weight Loss "Free to Live" guide, there's a section for ethnic foods. What they recommend for Thai:
Sauces: Use low-sodium soy sauce. Ask foods be prepared without MSG.
Appetizers: Satay, basil, vegetable rolls, steamed seafoods are all healthy appetizes. Clear soups are okay (yet can be very high in sodium), but try to stay away from creamed soups.
Salads: Salads are a great choice; ask for light dressing or for the dressing on the side.
Main Courses: Try to watch ordering curry dishes with coconut milk. Coconut milk is high in fat and is found in many Thai dishes.
Side Dish: Steamed rice is always a good choice (ask if they have brown rice)
Beverage: Coffee or tea for dessert is a low calorie choice. Drink water throughout your meal.
And they sum up the Do's and Don'ts:
Yes:
-Pad Thai with Chicken or Shrimp
-White Rice
-Chicken Ginger
-Chicken Satay
-Cashew Shrimp with Vegetables
No:
-Curry Beef
-Mee-Krob
-Todd Mun Chicken
-Crispy Taro Root
-Whole Fish, deep fried
And of course, wrap up any extras to take home!
Hope that helps, and above all else, enjoy yourself!