The last cool place that I went in Thailand was probably the most stylish. It's the Jim Thompson House, and it's awesome.
Jim Thompson was an American stationed in the Bangkok OSS office after World War II. He is credited with helping to revive the Thai silk industry. Thompson mysteriously disappeared in Malaysia in 1967. His house is now a museum showcasing his extensive art collection.
The house was probably the most tourist friendly place I visited while in Bangkok. There were free guided tours in multiple languages, and I found the staff to be very friendly and helpful. The little cafe's food was great, and the classy gift shop was air conditioned. I wouldn't mind living in that house for a week or four.
I think that's all I have to report on my trip. What a great country.