Ekkamai: First class air-con buses run roughly every hour between 02:00 and 21:30 and there's also a 24:00 departure. The cost is 205 baht and it takes 5.5 hours. These buses also service Chachoengsao.
Bangkok (Morchit): First class air-con buses depart at 09:30 and 15:45, cost 212 baht and take 5.5 hours.
Bangkok (Victory Monument): Mini-buses run hourly between 06:00 and 18:00 from the Tesco Lotus on Thaluang Rd further west from the bus terminal. The cost is 220 baht and it takes about 4.5 hours.