When I arrived in Thailand, and got out of the arrival gate at the airport, I saw a counter that said aiport limousine taxi, I read somewhere that I should only get in a taxi that was a government licensed one, so I got a ticket. It cost 650 Baht, The service was fine, it was a comfortable taxi and it got me to my accommodation fairly quickly. The driver did do some 'selling' to me however, he showed me some advertisements to some massage parlours which I refused and he recommended some other accommodation, however I had already decided on my accommodation.

Some alternative forms of transportation would be to catch a normal taxi - which should be about half the price or less to get into central Bangkok, you would probably have to talk down the price or ask the driver to use the meter, There are also buses and a train that you could use, which would also be considerably cheaper than a taxi. However you may have to do a bit of waiting and also you may need to find a person who can speak English to ask where the buses/trains go to.