New Bangkok airport codes
 

In case anyone who needs to know hasn't seen these posted elsewhere, the situation with airport codes at Bangkok appears to be as follows.

At the moment, the current arrangement is:-
BKK - Don Muang (the old airport)
NBK - Suvarnabhumi (the new airport)

With effect from 0300L on 28 September 2006 (the opening date for the new airport), these will change to:-
DMK - Don Muang
BKK - Suvarnabhumi

With thanks to FFHKG in this thread, amongst others.