Most foreign visitors to Bangkok arrive by plane. Bangkok's Suvarnabhumi International Airport (airport code: BKK) is the main gateway for visitors entering Thailand. Bangkok is a major hub and is serviced by all the big international carriers, as well as many regional airlines. However, please note that in March 2007, the old Don Muang Airport (airport code: DMK) re-opened for domestic flights. See the Bangkok airport guide at Asia-Airports.com for all the details about Bangkok's airports, including which airlines fly there, schedules, security and transfers.
Suvarnabhumi International Airport is located some distance from the center of town. The best way to get into town is by regular metered taxi. There's a counter just outside the airport terminal on level two (the same level you exit customs) to request a taxi, which are almost always waiting. You pay a 50 Baht surcharge on top of the metered amount when taking a taxi from the airport, plus any tolls. The trip to most city center hotels should take around 45 minutes to an hour, barring heavy traffic.
There's also an airport sanctioned 'limo' service, operated from its own counter just outside customs. The vehicles are not limousines in the western sense. The cars are just larger ordinary sedans, SUVs and vans. They have a fixed rate depending on what part of town you're going to. It's generally about double what you would pay a regular metered taxi.
Under no circumstances should you accept a ride from any touts or "unofficial" taxi services. Real taxis have a red and white TAXI-METER sign on the roof. All Airport Taxis are gray with green plates. Many people have been robbed by seemingly friendly people offering them a ride to "a good cheap hotel they know.