Additional information regarding the Airport transportation:
There are two lines running between the Airport and Phaya Thai / Makkasan station. One is the Airport Express, the other is the City Line (citiliner). Both are running on the same track but one stops at each station and the Express will go all the way to either Phaya Thai or Makkasan station. The fare for Airport Express is 150b (return valid within 2 weeks) and 90b (single); the fare for Cityline is 45b between Airport and Phaya Thai. The journey time is 15 mins and 30 mins respectively. You will find the route map here.