What companies offering domestic flights in Thailand and countries near it like Cambodia, Laos, Vietnam, Burma?
Currently needed directions are:
Bangkok-Angkor Chiang Mai- Angkor Angkor-Hanoi Hanoi-Saigon Bangkok-Bagan
Wikipedia is your friend, their airport articles are generally very up to date about who flies where. For example, the Siem Reap Airport article will (correctly) tell you the following connections from Siem Reap/Angkor:
Or try the friendly maps at OpenFlights:
In short, the only one of those sectors that's flown by a real LCC is Saigon-Hanoi, which is served by Jetstar Pacific.
I don't know that this is an SE-format question, or will really be answerable, but to add to the list:
Nok Air, Orient Thai Airlines (1-2-Go until they had a couple 1-2-crashes) .. are Thai Budget airlines, mostly domestic flights
Thai Airlines, Bangkok Air .. are 'normal', also mostly domestic
Air Asia has many routes in the area. Lao Airlines does what you'd imagine (regional flights b/w Lao and, mostly, capitals).
There are few worthwhile flights from CNX to anywhere else (you mostly either need to, or would be better off transferring through BKK/DMK).