The Tuk Tuk

Doing a similar job to the taxi is Thailand's ubiquitous tuk-tuk (ตุ๊กตุ๊ก). So named because of the sound of their engine, these are motorized rickshaws and are popular amongst tourists for their novelty value. Without any luggage, 3 people can fit into one fairly comfortably - it's possible to fit more in but it gets a bit cramped. Fares always have to be bargained for, and it is sometimes possible to bargain tuk-tuk drivers down to less than the taxi flagfall of 35B when they make good value. Most times, they offer no savings over a taxi, except perhaps if you're good at bargaining and can speak good Thai. The initial price they quote is likely to be well over the going rate, but it's easy to bargain it down to a more reasonable one if you know roughly the equivalent taxi fare.

It's essential to bargain the price with tuk-tuks before getting in. If you only ask after the ride, it's likely to end in a request for an ridiculous fare which can obviously lead to an unpleasant situation.

Just like taxi drivers, the tuk-tuk drivers mostly come from the rural northeast of Thailand and don't have to undergo any training (some will not even have passed a driving test), so don't be surprised if they sometimes have no idea where your destination is.

As tuk-tuks are open-ended, they expose passengers to the high pollution levels in the middle of Bangkok's roads and offer almost no protection in case of an accident. There is theoretically a ban on new tuk-tuks as they are so noisy and polluting, but it doesn't really seem to be being enforced at present.

--from http://www.into-asia.com/Bangkok/tuktuk/

*The key to bargaining with these guys was to just set a price about 1/3 of what they ask and not budge. It never failed. They're mad fun to ride in at night when there aren't many cars on the road, but Bangkok during the day is just ridiculous with traffic and the amount of exhaust fumes you're exposed to in these things.