Arrived by air in BKK, and had to take private taxi into town, due no current subway. There is a bus schedule into various areas of Bangkok, but the times are spread out. Price is a lot better than taxi, if you dont have to wait too long. Down by gate 8 at bottom floor. You can take advantage of the small food court there that the airport employees use. Very inexpensive.
Additionally, ther is a bus schedule into Pattaya as well, but the same problem.... they are spread at 2 to 4 hour intervals (same location)