A fragrant and colourful market along the Chao Phraya river, fresh flowers and vegetables are brought here every morning from surrounding provinces. The kaleidoscope of colours and pungent odour of flowers provide an exotic sensory stimulation. Its proximity to Chinatown and Pahurat make it a convenient stop while in the area; it's a bit of a walk though, so you may wish to hire a tuk-tuk instead.

Also, the market's main action takes place late at night or in the early morning, so to catch the action your best bet is to hire a taxi from other parts of the city, or at a nearby hotel.

How to get there: Take the Chao Phraya Express Boat to Pak Khlong Talat Pier; bus numbers 2, 5, 8, 53, 60, 73, and 512 also go to the area. From Chinatown, you can take a tuk-tuk for a short distance to the market (around 20 baht).
Items at market: Fresh vegetables and flowers (sold by wholesale or retail)
Hours: All day, although it is best to go between 02:00 - 04:00 when flowers first arrive from neighboring provinces
 

http://www.vivien-und-erhard.de/english/travel/thailand/bangkok/flo wermarket/index.htm

Pak Klong Talat, is the famous flower market of Bangkok. We liked to visit it every time at our earlier stays in Bangkok, but we never did it, because there were always many other fascinating places too, in this exciting city.
But at our last stop over in 2004 we went there and it was simply fantastic