There is a departure tax from BKK. It used to be 500Bht but has now risen to 700Bht. If your ticket was issued after 01/02/07 then it should be included in your ticket. If purchased prior to 01/02/07 then you will have to pay it prior to going through to departure Passport control. There is no arrival tax but make sure you keep the stub of your boarding card as the arrival Immigration will want to see it. If you pop it in your passport when you get on the plane it will save you time at immigration.