There are several airlines offering domestic flights in Thailand: THAI (Thai Airways), Air Asia, Bangkok Airways, Nok Air, Air Asia or Thai Smile, the low coat carrier of thai Airways which are the major companies and smaller ones like Kan Air to just mention the main ones. The most popular destinations by plane besides Bangkok are Chiang Mai, Phuket, Koh Samui, Krabi and hat Yai. The best rates are often offered by Air Asia and Nok Air (compare final prices with taxes and baggage fees knowing that for domestic flights in general the base price allows 15-20 kg of luggage). Some domestic flights depart from or arrive at Don Muang Airport in Bangkok (Nok Air and Air Asia flights for example). Check before departure and mention to your taxi driver ''Don Muang'' if your plane is scheduled there, if not by default if you just say ''airport'' he will drive you to Suvarnabhumi Bangkok International Airport. You can buy flight tickets in travel agencies or airlines agencies at the airport. But the most practical and cheapest way to buy plane tickets is by booking them on the airlines websites. Have a sweater to cover yourself. Sometimes the air conditioning in the plane is very cold.
Note that there are often special bus shuttles to take you from Suvarnabhumi Airport to Don Muang Airport. Ask information desk at the airport. Bangkok Suvarnabhumi has a brand new Airport Link, a skytrain line that takes you from Suvarnabhumi International Airport to downtown and vice versa.
Cities with airport: Bangkok, Buriram, Chiang Mai, Chiang Rai, Hat Yaï, Hua Hin, Khon Kaen, Koh Samui, Krabi, Lampang, Loei, Mae Hong Son, Mae Sot, Nakhon Phanom, Nakhon Si Thammarat, Nan, Narathiwat, Pai, Roi Et, Ranong, Pattaya, Phitsanulok, Phuket, Sakon Nakhon, Sukhothai, Suratthani, Trang, Trat, Ubon Ratchathani, Udon Thani