The Third Place is a very good coworking space in Bangkok. I think it's actually the only "official" coworking space you will find in the capital city. Of course you can always go to coffee place but I find it a lot more stimulating and confortable to a place that is dedicated to coworking. It's also a good chance to meet interesting people, potentiel clients or collaborators.
They also have food and drinks which is always convienent when you don't want to interrupt a productive day of work with a lunch break.
alex didn't write any chronicle yet about Bangkok