Air Asia were flying from Abu Dhabi for a while, but closed down almost as soon as they started.
You are kind of limited to Air Malaysia via KL (nice service) or Thai Air.
Emirates fly there, so do Cathay Pacific and Singapore airlines, but think they are rather expensive. Went to Cambodia a couple of years ago and flew Thai Air to Bangkok then Vietnam Airways to Pnomh Penh. Price was ok, but needed an 8 hour stopover in Bangkok which was too short to really enjoy it and too long to stay in the terminal. Spent the day looking up old friends and checking out the developments to the city as had not worked there for a few years.
Knight