I enjoy the JW Marriott buffet in their Marriott Cafe...breakfast, lunch, dinner or, the Sunday brunch. The Peninsula's buffet can be great if you can sit outside but the food selection tends to be hit or miss. For something different, you might be interested in trying the Sukhothai Hotel's chocolate buffet. I recently tried the lunch buffet at the Intercontinental. As with most of the good hotels in BKK, it was very good as well. Lastly, as already mentioned above, the buffet at Lord Jim's can be very enjoyable but be sure to get a table next to the windows overlooking the river.

On the negative side, I haven't really enjoyed the outdoor buffets are either the Oriental or the Shangri-La especially given the premium prices they charge.