One of the most fun and cheapest ways of getting around central Bangkok is by express boat along the Chao Phraya River. The 21km route is served by 65 boats and operates between 6:00 am to 7:30 pm on weekdays and 6:00 am to 6:40 pm on weekends and holidays. Current prices are from 9 baht (Local line for distance within one zone) to 30 baht (for green-yellow flag trip on its entire route from Pakkret to Sathorn), depending on the type of boat and the distance travelled. I took the service a couple of times from the BTS Skytrain station at Saphan Taksin which is near the Sathon pier to Phra Pin Klao Bridge pier in order to get to the Southern Bus Station instead of getting a taxi through the centre of Bangkok. It's also a very scenic trip as you pass by the Grand Palace, Wat Arun, churches, Wichai Prasit Fort and some temples along the way...