On a recent trip to Bangkok, I went to the following:
The Local - Sukhumvit Soi 23 (Thai)
First visit. The dinner we had was so wonderful, we went the 2nd time 2 days afterwards to celebrate my sister's birthday. Food excellent, atmosphere charming. Try the Panang ribs and Tamarind River Prawns.
Secret Garden - Sathorn
First visit. While walking from W I stumbled into this restaurant and had a lovely lunch. Mostly local crowd from offices nearby. No traditional Thai desserts but great looking cakes.
Eat Me - Silom
2nd visit. Did not disappoint again. I had a lovely tomato salad and rack of lamb. Very popular spot.