I would say that their soups would be good, well the ones that don't have coconut milk in them, as they're essentially just vegetables, meat, herbs and a bit of stock. I can't remember the proper name of the soup now!
Pad Thai would be really good if you like noodles, as it's just noodles (either egg noodles, or rice noodles) cooked in egg with beansprouts, some veg and whatever meat you choose.
There are also options like chicken and cashew nut which should be fairly low in sins with some boiled rice.
Generally thai food is really healthy, the only bad ingredient they use is coconut milk. I lost about 2 stone when I travelled in thailand without even trying as the food is so healthy.