Tourist Authority of Thailand website provide a lot of general and useful information about the country.

http://www.tourismthailand.org/home.php

Thai Airways is the main airline in Thailand. 

www.thaiair.com/

Air Andaman is an Airline company operating mainly in the south and north of Thailand.

http://www.airandaman.com/

Thai meteorological Department. Weather forecast.

http://www.thaimet.tmd.go.th/eng/default.asp

Tourist Police

http://tourist.police.go.th/eng/index.html

Thai Farmer Bank Exchange rate

http://www.kasikornbank.com/

Gecko Travel is one of the best Tour company for South-east Asia.

http://www.geckotravel.com

www.travelfish.org 100% original Asia travel intelligence authored by dedicated travellers who know what they're talking about.

State railways of Thailand operate all trains in the country. Infos, time table and fares.

http://www.railway.co.th/httpEng/

The cheapest airfares for flights in and around Thailand, Malaysia and Singapore.

http://www.airasia.com

Nok Air, Competition with Air Asia for the cheapest fares on internal Thai flights.

http://www.nokair.com

http://www.globalairlineticket.com