Another thing I missed in Bangkok the first time around was Jim Thompson's House.
You can read about Jim Thompson here, but he was basically an American businessman who fell in love with Thailand, collected some old Thai houses from all over that he put here in Bangkok, revitalized the Thai silk industry, and then disappeared into the jungle in Malaysia, never to be seen again.
This is his house:
It's full of antiques and there are all sorts of silk things for sale.
The garden is lovely too.