Here are some Airline Links and Cities serviced by each airline. Although there are several operating airports in Isaan it can still be a little tricky finding a flight out of certain airports on certain days: I recommend making reservations well in advance.

Thai Air Asia:Link
Udon Thani
Ubon Ratchathani


PB Air: Link
By PBAir:
Roi-Et
Buriram
Sakon Nakhon
Nakhon Phanom

Code share with Thai Airways:
Khon Kaen
Udon Thani
Ubon Ratchathani

Nok Air: Link
Ubon Ratchathaini
Udon Thani


Thai Airways: Link
Sakon Nakhon
Nakhon Phanom
Khon Kaen
Udon Thani
Ubon Ratchthani


Note: If you want to go to Korat (Nakhon Ratchasima) you need to take the train; the airport is closed and will remain closed for some time. Phoenix Air thought about flying in there but problems in BKK prevented it from happening.