
Baan Kanitha & Gallery (Thai)
69 South Sathron Road @ Soi Suan-Plu
Very authentic Thai food. Their set lunch at BHT 230 (weekday only, I believe) is a true bargain, considering a Thai Iced Coffee will set you back BHT 120 further.
Baan Klang Nam (Thai Seafood)
3792/106 Soi 14, Rama III Road
This riverside restaurant is a must-have dining experience in Bangkok. Seafood is their specialty and special it is. Their curry crab is beyond imagination. The location is quite remote, so taxi ride is a must. Ask your hotel concierge for assistance.
Chinatown Dining - Shark Fins & Bird Nest (Chinese)
Yaowarat Road
There are really only 2 reasons you eat Chinese food in Bangkok: shark fins soup, and bird's nest. Both are Chinese delicacies, and both are available locally for a fraction of the price and with high quality. There are a lot of restaurants in Chinatown serving both, so just pick one.
Food Court (Thai and other)